A line with a gradient 3/2 passes through the point (3, t) and (t, 8). Find the value of t, hence express the equation of the line in the form ax + by = c (where a, b, and c are constants).
a) t = 4; 3x + 2y = 18
b) t = 6; 2x + 3y = 15
c) t = 2; 2x + 3y = 12
d) t = 5; 3x + 2y = 16