I'm having problems with the following equation:

```
\[\frac{dT(t)}{dt} =-1^{\circ}F \text{per hour}\]

```

it displays:

[![enter image description here](https://i.stack.imgur.com/6khKi.png)](https://i.stack.imgur.com/6khKi.png)

How do I make "per hour" in normal text form rather than italicized?