If a 36-inch yardstick casts a 21-inch shadow, how tall is a building with a 168 foot shadow?

The sun must be very low in the sky, as a 24foot building would cast the 168-foot shadow.

Always be careful that the units of your calculation are consistent. It is a common trick in word problems to see if you are attentive.
It is best to stay in feet rather than inches in this problem.
The 36 inches is equal to 3 ft.

I prefer to just use a proportion to solve:
3/21 = x/168 Using cross products we calculate x = 24 ft

if you use photomath right away it will give you the answer not like this app that you have to wait for people.

yes because there is exactly one y value for every x value

for function there can't be more than one value for every x value