Use substitution to solve the system of equations. Which letter choice is the answer?
y = 4.5x + 7.5
y = –3.5x – 4.5
A. x = –1.5, y = –0.75
B. x = 1.5, y = 0.75
C. x = 1.5, y = –0.75
D. x = –1.5, y = 0.75

constant of proportionality = 3 and the equation is c = 3p.

step-by-step explanation:

c = kp   where c = amount of caffeine in mg., p = oz of pepsi and k is the constant of proportionality.

substituting the values given:

24 = 8k

k = 3.

the same value of k will be obtained if we substitute the other given values.