Answer: m∠5 = 75°.
Explanation:
We know that lines A and B are parallel, and angles 1 and 5 are formed by the same line intersecting the parallel lines.
We know that:
"When a line intersects two parallel lines, corresponding angles are formed, such that we could think on four quadrants, the angles in each quadrant are equivalent between them"
Well, here we can see that angle ∠1 and angle ∠5 are formed by the same line, and both are in the same quadrant (would be the third quadrant if we use standard notation)
Then the measure of ∠1 is the same as the measure of ∠5
And we know that m∠1 = 75°
Then we must have that m∠5 = 75°.