Question

Building A was built 20 years before building B and 20 years after building C. In 10 years, building C will be 20 years younger than the combined ages of buildings A and B. What is the present age of each building?

I started to set up the problem and solve it, but my solution doesn't make any sense.

Buildings Now in 10 yrs.
A x-20 (x-20)+10
B x x+10
C x+30 (x+30)+10

Building B
[(x+30)+10]-20=(x-20)+10+x+10
x+ 20=2x -> x-x+20=2x-x
x=20 <- Doesn’t Make Any Sense for B