Given point A: (5,9), point B: (d,15) and the gradient of line AB is 3... what is the value of d?

First use the gradient equation for a line: difference in y over difference in x:dy/dx = gradienttherefore: (15-9)/(d-5) = 315-9=3(d-5)6=3d-1521=3dtherefore d = 7