Chapter 7 Exponential and Logarithmic Functions - 7.7 Write and Apply Exponential and Power Functions - 7.7 Exercises - Skill Practice - Page 533: 8

$y=10*4^x$

$$640/40 = 16 $$ We must find the square root of that because after subtracting the x values (3 and 1), we get 2. That gives us 4. The initial value is 40, and 40 divided by 4 is10. In conclusion, the answer thus is, $y= 10*4^x$