So in order to find x you need to make an equation like so.
6x + 4x + 10 = 90 (the 90 is from the right angle)
You then combine like terms.
10x + 10 = 90
To isolate the variable you need to subtract 10 to both sides leaving you with...
10x = 80
Then you divide 10 from both sides and your final answer is x=8.
Lets check our work shall we???
6(8) +4(8) + 10 = 90
48 + 32 + 10 = 90
48 + 42 = 90
90 = 90
It is a solution! Yayyyyy!!!! So 8 is your answer. I hope this helps love! :)