Question

For what value of x is line m parallel to line n?

Answer 1

x = 42

Explanation:

You want to know the value of x that makes alternate interior angles 105° and (3x-21)° congruent.

Congruent angles

When alternate interior angles are congruent, the lines forming them are parallel. Congruent angles have the same measure, so we want ...

3x -21 = 105

3x = 126 . . . . . . add 21

x = 42 . . . . . . . divide by 3

The value of x is 42 when the lines are parallel.