Find the measure of ∠D if ∠A = 5 2 x + 30 ∠B = 7 2 x + 40 ∠C = 9 2 x + 10 ∠D = 5 2 x + 20

okay so my answer may or may not be correct I am sorry if it is not. 
<A= 52x+30
<B= 72x+40
<C= 92x+10
<D= 52x+20
I put <A and <B together and <C and <D together<A and <B :
 52x+30 = 72x+40
-52            -52          30 = 20x+40         -40           -40
-10 = 20x/20   /20-0.5 = xwhen you put it into the equation as 52(-0.5)+30 you get 4, and when you put it in 72x+40 you also get four. 
Now for  <C and <D 92x+10 = 52x+20-52           -5240x+10 = 20        -10   -1040x = 10/10      /10x=4