In the given figure, AOC is a straight line. Find x.

 

We know that ∠AOB and ∠COB are linear pairs.

It can be written as, ∠AOB + ∠COB = 180^o

Substituting the values, we get:

=> x + 25^o + 3x + 15^o = 180^o

=> 4x + 40^o = 180^o

=> 4x = 180 – 40 = 140^o

=> x = $\frac{140}{4}$ = 35^o