Noob problem that I cannot resolve and couldn't find a solution. Values between curly braces not rendering in component Content and component Total. I checked the JSX rules but I'm missing something.

```
import React from 'react'

const App = () => {
    const course = {
        name: 'Half Stack application development',
        parts: [
            {
                name: 'Fundamentals of React',
                exercises: 10
            },
            {
                name: 'Using props to pass data',
                exercises: 7
            },
            {
                name: 'State of a component',
                exercises: 14
            }
        ]
    }

    const Header = () => {
        //const course = 'Half Stack application development'
        return (<div>{course.name}</div>)
    }

    const Content = () => {
        return (
            <div>
                <Part1/>: {course.parts[[0].exercises]} exercises.<br />
                <Part2/>: {course.parts[[1].exercises]} exercises.<br />
                <Part3/>: {course.parts[[2].exercises]} exercises.<br />
            </div>
        )
    }

    const Part1 = () => {
        //const part1 = 'Fundamentals of React'
        return (<>{course.parts[[0].name]}</>)
    }

    const Part2 = () => {
        //const part2 = 'Using props to pass data'
        return (<>{course.parts[[1].name]}</>)
    }
    const Part3 = () => {
        //const part3 = 'State of a component'
        return (<>{course.parts[[2].name]}</>)
    }

    const Total = () => {
        //const exercises1 = 10
        //const exercises2 = 7
        //const exercises3 = 14
        return(
            <div>
                Number of exercises: {course.parts[[0].exercises]+ course.parts[[1].exercises] + course.parts[[2].exercises]}.
            </div>
        )
    }

    return (
        <div>
            <Header></Header>
            <Content></Content>
            <Total></Total>

        </div>
    )
}

export default App

```

The above script render this on the browser, values should appear before ": exercises" in the lines 2,3,4 :

```
Half Stack application development
: exercises.
: exercises.
: exercises.
Number of exercises: NaN.

```