When a ray bisects an angle, it divides said angle in half. This means that the two new created angles will have the same measurement and when added they should be equal to the larger one. With this in mind we can find mABX as shown below:
We were given the values for mABC and mCBX, so we use those in the expression above and solve for the value of mABX. We have:
The value of mABX is "4x + 11".