Since B and C are congruent, that means that 4x+10=x+34. Using the addition property of equality, I challenge you to solve for x! After you do that, you can note that all the angles in a triangle add up to 180, so 4x+10+x+34+angleA=180. When you find x, you can substitute that in.
If you need help with the addition property of equality for variables, here's an example - 5x+23=4x+3. Subtracting 3 from both sides, we get 5x+20=4x. Next, we can subtract 5x from both sides to get -x=20 and divide both sides by -1 to get x=-20.
Good luck, and feel free to ask with any questions!
