Using formals to find information

Formulas are useful to give us information we may not be able to know otherwise.

Example:
D = rt

where
D = distance
r = rate
t = time

The formula gives us the distance we have traveled accounting for rate and time.

Consider:
We travel 70mph for 7 hours, how far have we gone?

D = 70 * 7 = 490 miles!

Since we know how to simplify expressions and solve for variables we can use the formula to answer many questions.

Consider:
How fast would we have to go to travel 490 miles in 7 hours?

490 = r * 7

r = 490 / 7 = 70 mph