Im pretty sure it can. 20 +20 = 40. if that helps...
We can see that for every 1 hour he increases 10 miles in his distance, so we can say it's constant, he started at 0 and increased 10 miles per hour.
Alternative C.
Subsitute -4y for x
-4y+6y=18
2y=18
divide both sides by 2
y=9
sub back
x=-4y
x=-4(9)
x=-36
(x,y)
(9,-36)
None of those. ∠BAD = 180º - 90º - 55º = 35º, because ABC is a right triangle.