Question

Solve the matrix equation 2x + 5y = 1
x + 3y = 0 for y.

A)1
B)3
C)-3
D)-1
I chose D

2x + 5y = 1
y = 5 - 2x
x + 3(5 - 2x)= 0
x + 15 - 6x = 0
7x = 15
x = 15/7
I know that's wrong I don't know what to do

Answer 1

Your very first step is incorrect. Try this:
x + 3y = 0
x + 5/2 y = 1/2
Now subtract the last eq. from the first.
y/2 = -1/2
y = -1

Answer 2

your solution is "riddled" with errors

2x + 5y = 1 solved for y is y = (1-2x)/5
not y = 5 - 2x like you had.

Even if it had been right, x + 15 - 6x = 0
becomes
-5x = -15 , not 7x=15 like you had

lets start over.
Why not solve the second equation for x? (look for the "single" variable)
x = -3y sub that back into the first
2(-3y) + 5y = 1
-y = 1
y = -1 looks like your D was the right guess.

Answer 3

- 15 x ² + 2x + 13 = 0