Does it say what the measures are equal to ?
the measure of a central angle and its arc are equal 4x + 12 = x + 13
does it = -3?
Combine like terms which are 4x and x which is equal to 5x
Then it would be 5x+12+13 which would end up leaving you with 5x=25 then divide 5 on both sides & you will find the value of x