Answer:
12.8 seconds
Step-by-step explanation:
Create a proportion where x is the number of seconds for 80 feet
= 
Cross multiply and solve for x
25x = 320
x = 12.8
So, the answer is 12.8 seconds
X = 15
X + 90 = 7x
X = 7x - 90
X - 7x = -90
-6x = 90
Divide both sides by -6
X = 15
C. The square root of 144