Lines m and n are perpendicular and x is 15 solve for x

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'

Eliza wants to make $10,000 from her investments. she finds an investment account that earns 4.5% interest. she decides to deposit $2,500 into an account. how much money will be in her account after 14 years?

X/y + 4y/x divided by x/y - 2y/x explain as in depth as you can how you simplfied the fractions. i don't know where to start on this : /