Given, in the figure PR and PS are two tangents. They meet at P. Here angle P given. ∠P = 42°.
If we take a straight line PQ, it will create two triangles.
We can see here angle R and angle S both are right angles.
As here two triangles, so sum of all the angles of the triangles is 
Now if we subtract the two right angles we will get,

That means ∠P+∠Q = 180°
If we substitute the value of angle P we will get,

We can get angle Q by subtracting 42 to both sides. We will get,



So we have got angle Q, the measurement of ∠Q = 138°.