Here are some basic formula modules.
The first example is a freelancer cost estimator ( rate x hours + tax ) with a fixed/unchangeable rate field.
The second example is an addition with the result squared formula a+b=c^2
The third is a square root formula that rounds up/down to the closest whole number.
Note the way the examples below are styled are using the standard template module class suffix. No custom CSS has been added. You can use your own templates style or create your own CSS.