I need help with this ​

20

Step-by-step explanation:

Hello There!

So first we need to determine what the formula for area of a trapezoid is

where a and b = bases and h = height

the given information is the area and the two bases

so we plug in the given information and solve for h

divide each side by 9

we're left with

h=20

so we can conclude that the height is 20

x = -3

y = -18

step-by-step explanation:

to solve by substitution, substitute one variable and solve for the other. then substitute again to find the remaining variable.

x-1/3(3x-9) = -3 since y=3x-9 substittute y.

x-1/3(3x-9)=-3

x + x +3 = -3

2x+3=-3

2x+3-3= -3-3

2x=-6

x=-3

substitute again into y=3x-9

y=3(-3)-9

y=-9-9

y=-18