Answer:
for 18 x is 6 and for 20 it is 11
Explanation:
For 18, since -1+2x and 5+x is the same thing, set up and equation. WE can simplify to -1+x=5 and then we get x=6
For 20, 18 is 11 since 18=-4+2x. If we simplify we get 22=2x then we can use algebra to say that x=11
Hope this helps :)