To work out the total of interior angles you do (n-2) x 180. n is the amount of sides so substitute it and (5-2) x 180 = 540 degrees. Now, add known values and subtract it from 540. 540-350=190. The rest of the angles must equal 190 and your unknown is 4x+10. To work out 4x you must do 190-10 which is 180 and divide 180 by 4 to get a final answer of 45 degrees.