The value of x is: 9
How to find the missing angles?
The exterior angle theorem states that the measure of an exterior angle of a triangle is equal to the sum of the measures of the two remote interior angles of the triangle.
In other words, if you extend any side of a triangle, the exterior angle formed is equal to the sum of the two opposite interior angles.
Thus, we can say that:
7x + 5 + 48 = 13x - 1
7x + 53 = 13x - 1
6x = 54
x = 9