Help with algebra 2 i dont know how to do this

Which expression can be used to determine the slope of the line that passes through the points -6, three and one, -9

Sum is 17 and their difference is 3

Mr. and mrs. wallace have decided to buy a car for $21,600. they finance $15,000 of it with a 5-year auto loan at 2.9% arp. what will be their monthly payment be? a. $268.20 b. $268.86 c. $269.54 d. $387.16 (monthly car loan payment per $1,000 borrowed) i need !