20 POINTS Write an algebraic expression or equation
The product of nine and the sum of a number and four.

9(4 + x)

Step-by-step explanation:

the product of 9

9 *

the sum of a number (x) and four

x + 4

the product of 9 and the sum of a number and four

9 * (x + 4)

step-by-step explanation:

the ratio of red paint to blue paint is always 9/7. that means that, whatever x's value, (4x+12)/(4x-4) has that same ratio. so, set up an equation and cross-multiply to solve for x:

9/7 = (4x+12)/(4x-4)

9(4x-4) = 7(4x+12)

36x - 36 = 28x + 84

8x - 36 = 84

8x = 120

x = 15