Answer:
x = 3/2
y = 5/2
Explanation:
x + y = 4
x = y - 1
substitute y - 1 in for x in the first equation, to find y
y - 1 + y = 4
2y - 1 = 4
add 1 on both sides
2y - 1 = 4
+1 +1
2y = 5
divide by 2 on both sides
2y/2 = 5/2
y = 5/2
subtitute y in for the second equation, to find x
x = 5/2 - 1
x = 5/2 - 2/2
x = 3/2
so x = 3/2 and y = 5/2
to double check, plug x and y in the first equation
3/2 + 5/2 = 4
8/2 = 4
4 = 4