Concepts Used:
Finding x:_____________________________________________
From the Exterior angle property, we know that the measure of an exterior angle is the sum of the 2 opposite interior angles
So, using the property
(3x-10) = (25) + (x + 15)
3x - 10 = 25 + x + 15
3x - 10 = 40 + x
3x-x - 10 = 40 [subtracting x from both sides]
2x - 10 = 40
2x = 50 [adding 10 on both sides]
x = 25 [dividing both sides by 2]
Hence, the value of x is 25
