Average rate of change: slope
First, we have to calculate the y values, from the x values given:
x1=4
Replace on the function:
f(x)= 10 (2)^x/4
f(4)= 10 (2)^4/4
f(4)= 10 (2)^1
f(4)= 10 (2)
f(4)= 20
y1= 20
x2=12
f(12)=10 (2)^12/4
f(12)= 10 (2) ^3
f(12)= 10 (8)
f(12)= 80
y2= 80
Apply the slope formula:

Replace:

rate of change : 8.75