4(2x-7)=8x-28
4(-4x+18)=-16x+72
(8x-28)-(-16x+73)
24x+45
75% of what is 0.90
0.75x = 0.90
x = 0.90/0.75
x = 1.20 <== restaurant pays $ 1.20 wholesale
0.15 is bigger, cause the second digit after the decimal is bigger. You would have to add another 0.025 to 0.125 to bring it up to 0.15
So for this function we will be using the quadratic formula, which is
, to solve. a = x^2 coefficient, b = x coefficient, and c = constant. Using our equation, we can solve for the zeros (x-intercepts) as such:

In short, your x-intercepts (rounded to the hundredths) are (1.92,0) and (-3.92,0).
The total R value is computed from the R-values of the components in the stack as ...
(inches of wood)*(R-value of wood) +(inches of fiberglass)*(R-value of fiberglass) +(inches of foam)*(R-value of foam)
= (4 in)(2 /in) +(2 in)(4 /in) +(3 in)(5 /in)
= 8 +8 +15
= 31
The total R-value of the wall is 31.