Answer:
x = -18
y = 4
Explanation:
x + y = 4
2x + 3y = 30
You can do any math operation to each side of the equal sign as long as you do the same operation to both sides.
change x + y = 4 to x = 4 - y
Now substitute (4 - y) into the second equation, in place of x.
2(4-y) + 3y = 30
multiply the 2(4-y) part:
8 -2y + 3y = 30
simplify:
8 + y = 30
subtract 8 from each side:
y = 22
now substitute the value of y back into the first equation to solve for x:
x + 22 = 4
subtract 22 from both sides:
x = -18
Check:
x + y = 4
22 -18 = 4
4 = 4 (this checks)
2(-18) + 3(22) = 30
-36 + 66 = 30
30 =30 (this checks also)
PS: you could have solved for y first if you had wanted to. The results would be the same.