kristy had two brothers and 2 sister the little sister name kylie was 8 years old the big sister name kaylie is 12 years old the big brother name jay lay is 13 years old the little brother is 10 years old but they mom let hem buy what ever they wanted she gave each 10$ and 9 cents how many money did she paid

i think $54.5

Step-by-step explanation:

i did 5 times 40 and 5 times .9

An exponential function is a function with a number that is positive and is not 0 or 1 that has x as its power. For example, f(x)=2^x
f(x)=2x-3 is not an exponential function, because there is no exponent.
f(x)=(89-120)*3/4x. Still not exponential.
f(x)=3.5^x. That is an exponential function.
Just remember that the number in the base cannot be negative because we would get the number i,  and it cannot be 0 or 1 because we would get 0 or 1 respectively. 
Hope that helped! :D. Comment if you have any questions.