We know that angles in a triangle sum to 180°, and are already given the measurement of a right angle. Therefore, we know that the other two missing angles add up to 180°-90°= 90°. So, we can place the given terms and this information into an equation and solve for x:
(3x+8)+(5x-14)=90
3x+8+5x-14=90
8x-6=90
8x=96
x=12
Measurement C is 3x+8, so just substitute x:
C=3(12)+8
C=36+8
C=44°