if 5x + 7y = 18 and 2x - 4y = 6, what is the value of 7x + 3y?

a. 7
b. 12
c. 19
d. 24
e. 31

2 answers

take the 2nd and divide by 2
x - 2y = 3
x = 2y+3
plug that into the first
5(2y+3) + 7y = 18
10y+15+7y=18
25y=25
y=1
then x = 2(1) + 3 = 5

now that we have x=5, and y=1
evaluate 7x+3y
35