Question

X is partly constant and partly variable.when Y=5, x=19 and when y=10, x=34 find x when y is 7

Answer 1

x = ky + c

when Y=5, x=19 ---> 19 = 5k + c
when y=10, x=34 ---> 34 = 10k + c
subtract them:
15 = 5k
k = 3
in 5k+c = 19
15 + c = 19 ---> c = 4

x = 3y + 4

so when y = 7 .....