Find the slope of the line through each pair of points (19,9),(15,-3)

Pls! does anybody know a shortcut for answering these types of questions in the future?

What expression is equivalent to 42x-56y

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.