Watch closely. I'll try to go slow.
Stop me if I go too fast, or if I do anything that you don't understand.
Ready ?
You said d = r t
Divide each side by ' t ' : d / t = r
The answer is B (Sorry for the bad handwriting.)
I would set D = 816000 and then solve
2x^2 + 3xy - 4y^2 when x = 2 and y = -4
= 2(2)^2 + 3(2)(-4) - 4(-4)^2 = 2(4) + (-24) - 4(16) = 8 - 24 - 64 = -80