Please help

will mark brainlist

What is the number 321,000,000 in scientific notation? also what is the number? ?

What is the solution to this system of equations? y= 2x - 3.5 x - 2y = -14

Melissa is purchasing a $160,000 home and her bank is offering her a 30-year mortgage at a 4.9% interest rate. in order to lower her monthly payment, melissa will make a 20% down payment and will purchase 3 points. what will her monthly mortgage payment be? a. $645.98 b. $650.46 c. $662.93 d. $606.69