If we know that a line passes through P (2a, 3b) and Q (4b, 6a) and a is not zero, we can find the slope of the line

If we know that a line passes through P (2a, 3b) and Q (4b, 6a) and a is not zero, we can find the slope of the line

When 2A = 4b, PQ is perpendicular to the x-axis, and the slope does not exist
When 2A does not = 4b, the slope k = (6a-3b) / (4b-2a) = 3 (2a-b) / [2 (2b-a)]