x is partly constant and partly varies as y when y=2, x=30 and when y=6, x=50. Find x when y=3

Answer 1

x = c + ky
when x=30, y=2 ----> 30 = c + 2k
when x=50, y=6 ----> 50 = c + 6k

solve these two equations for c and k, sub back into x = c + ky
then find x when y = 3

I suggest subtracting the two equation to solve for k

Answer 2

I don't get it