Answer:
1. I assume that stretching vertically by factor of 2 means that every point on the transformed curve is twice as far from the x axis as the original curve.
Imagine that you have plotted y=5x. you want to change the y scale so that each point on the original curve is two times as high. For example, one point on the original curve is (1,5). This point must be relocated to (1,10). Similarly, the point (2,10) on the original curve must be relocated to (2,20).
You can see that these relocations are accomplished if we transform the function to y=2(5x)=10x.
Explanation:
hope this helps! even though it's just the first one...