Answer:
2x + 2y = 24
Step-by-step explanation:
You have to isolate y and then use substitution.
x + y = 12 and y = x - 1
-x -x
y = -x + 12 and y = x - 1
-x + 12 = x - 1
+x +x
--------------------
12 = 2x - 1
+1 +1
----------------
13 = 2x
2x = 13 [ divide both sides by 2]
x = 6.5
Now, you have to plug x (6.5) into y = x - 1.
y = x - 1
y = 6.5 - 1
y = 5.5
Finally, plug both x (6.5) and y (5.5) into 2x + 2y.
2x + 2y
= 2 (6.5) + 2 (5.5)
= 13 + 11
= 24