Question 762911
since the relationship is linear we know that we plot the relationship on a co-ordinate system.  we would have a line going through the points

(20, 12) and (30, 15)

if we fill in the x and y co-ordinates on the equation for a line
y=mx+c we get teo equations which can be solves simultaneously

15=30m+c
12=20m+c

minus one from the other, to get m=3/10
fill this in into any of the two equtions to get c, whcih is 6.

thus the realtionship, is the linear equation
y=3/10x+6