Combine DE and EF together for 47 + 3x + 10 for 57 + 3x
Then combine like terms from both sides, so 57 + 3x = 9x - 39
After your adding and subtracting you should get 96 = 6x
After dividing both sides by 6 to get x by itself, you get 16 = x
Plug 8 in for x into 3(16) + 10 for a final answer of 58.
You can check doing 47+58 = 105 by making sure both sides equal.