//5. Use substitution to solve the system of equations 3x - y = 4
2x - 3y = 9
Solution: (
)

(3,5)

Step-by-step explanation:

y=3x-4

2x-3y=-9

2x-3(3x-4)=-9

2x-9x+12=-9

7x=21

x=3

y=3(3)-4

y=5

"y varies directly as x" means y = kx

you do not know what k is yet, other than that it is some constant number.

Now plug in the given values, y=12 when x=4, in the equation

12 = 4k

=> k = 3

Now rewrite the equation with the k value you just found

y = 3k

Substitute 18 in place of x

y = 3(18)

y = 54