D=45h
For example: 45mph times 2 hours equals 90 miles traveled
The answer is 7:17 because when you add them together it equals 7:17.
and 
use the second expression to calculate the left-hand side of the first equation:

Add 10 to both sides if this equation to get

and divide both sides by 2

this proves that x = 17, give the two initial equations
Y = -3x + 6
y - 6 = -3x
-1/3 y + 2 = x
z = x -3
z = -1/3 y + 2 -3 = -1/3 y - 1
set z = 0
-1/3 y = 1
y = -3
set y = 0
z = - 1
Ex: you can do 5-3 by putting a dot on the five and looping back 3 spaces. Hope it helps!