y = mx + b, m = slope and b = y-intercept
Because you don't have the y-intercept, you take the equation and replace x and y with the values given, then solve for b and replace b in the original equation with the value found.
y = 2/3x + b
0 = (2/3)(-3) + b
0 = -2 + b
2 = b
y = 2/3x + 2 is the answer
