Passes through -1, 10, slope equals -6

I'm terrible at math any here is appreciated.

Tamera puts 15/4 gallons of gasoline in her car. which mixed number represents the gallons of gasoline? a) 2 3/4 gallons b) 3 1/4 gallons c) 3 3/4 gallons d) 4 1/2 gallons answer it's worth a lot of points!

Solve for n? [tex]z = \frac{3}{4} mn[/tex]