What is the % of 21/40

Astudent simplified a rational expression as shown.

Find the slope and the y-intercept if there's one and the equation of the line given these two points( 3, 2) and( 3, -4)

Diane’s bank is offering 5% interest, compounded monthly. if diane invests $10,500 and wants $20,000 when she withdrawals, how long should she keep her money in for? round to the nearest tenth of a year.