y = mx + b
slope(m) = 3/4
(3,7)...x = 3 and y = 7
now we sub and find b, the y int
7 = 3/4(3) + b
7 = 9/4 + b
7 - 9/4 = b
28/4 - 9/4 = b
19/4 = b
so ur equation is : y = 3/4x + 19/4
if point A (x,5) lies on the line.....
y = 3/4x + 19/4......when y = 5
5 = 3/4x + 19/4
5 - 19/4 = 3/4x
20/4 - 19/4 = 3/4x
1/4 = 3/4x
(1/4) / (3/4) = x
1/4 * 4/3 = x
4/12 reduces to 1/3 = x......so point A is (1/3,5)...with x being 1/3