"Supplementary" angles add up to 180°.
Opposite angles are supplementary, so . . .
(12x - 4) + (19x - 2) = 180°
Clear the parentheses: 12x - 4 + 19x - 2 = 180°
Add up all the x's on the left side: 31x - 4 - 2 = 180°
Add up the plain old numbers on the left side: 31x - 6 = 180°
Add 6 to each side: 31x = 186°
Divide each side by 31 : x = 6°
Well ! Now that you know that x = 6° . . .
Angle EPC is (12x - 4)°
That's (12·6 - 4)°
Which is (72 - 4)°
Which is 68°
