Idon't get it ?
which transformation will map figure h onto figure h'?
a. reflection across the y-axis
b. vertical translation of 10 units
c. vertical translation of 15 units
d. reflection across the x-axis

For this kind of questions, what you can do is to find a point on the figure and see what translations it does.

For example, you can find the point (4,2) on the figure H. And then look at each choices to see if the statement is correct.

For this question, the answer is B. The point (4,2) finally change to the (4,-8) on the figure H'. It has a vertical translation of 10 units down.