Actually the rise is neg 1 and the run is pos 2 so -1/2 would be the answer
The area of the right triangle =

b = base = SV = 12.3
h = hight = HL = 24.6
A = area

Your max amount for this is $20. Let's say x represents the number of gallons.
20 ≥ 3.2x
x = 6.25 gallons
If they're asking for integers or whole numbers, you'd round down to 6 because you only have enough money for 6 full gallons. If you rounded up to 7, you wouldn't be able to fill it up completely because then you'd be over your $20.00 budget for gas.
5x-y10 We're basically just multiplying the 5 by x and the y by 5 and -2.
(5/x= 5x) + (y/-2/-5)