You have an isosceles triangle, that is, you have a triangle with two equal angles and two equal sides.
Then, angles N and M have the same measure.
In order to find the measure of angle M, you first equal the given expressions for such angles:
2x = x + 30
solve the previous equation:
2x = x + 30 subtract x bot sides
2x - x = 30 simplify like terms
x = 30
next, replace the previous value of x into the expression for angle M:
x + 30 = 30 + 30 = 60
Hence, the measure of angle M is 60°
