Answer:
a. x + 4 = 12; x = 8
b. 2x + 4 = 12; x = 4
Step-by-step explanation:
a. for x = 8; let unknown be k
k + 4 = 12
k = 12 - 4 = 8
k/x = 8/8 = 1 which is the coefficient of x
therefore x + 4 = 12 when x = 8 is correct
b. for x = 4
k + 4 = 12
k = 8
k/x = 8/4 = 2 which is the coefficient of x
therefore 2x + 4 = 12 when x = 4 is correct
