We know that m and n are parallel.
Then, x is supplementary of 145 degrees.
This is because the adyacent (and supplementary) angle of x is, with the angle of measure 145 deg, alternate exterior angles and have the same measure.
Therefore, x and the angle of 145 degrees are also supplementary.
If they are supplementary, they add 180 degrees, so we can write:
x = 35 degrees