Efficiency of calling other classes
Simplify multiple conditions using a switch

Whenever multiple conditions depend only on the value of a single variable,
consider using a switch instead to simplify:

switch (ans) {
    case 1:
        Quadratic.CalcQuad();
        break;
    case 2:
        CompInt.CalcInt();
        break;
    default:
        System.out.println("That was not an option.");
}


Naming

The common convention is to use camelCase for function names.
The method names CalcQuad and CalcInt violate that.

It also seems that the class names could be better.
If you spell out their purpose, the names won't be much longer but a lot more intuitive and unambiguous, for example:


Quadratic -> QuadraticCalculator
CompInt -> CompoundInterestCalculator


And then the methods that do the calculation can be simply calculate in both classes, without including the type of calculation, which is already included in the class name.

Alternatively, you could use a single Calculator class with calculateQuadratic and calculateCompoundInterest methods.