The total cost (y) of buying cherries per pound (x) is shown in the chart.Strawberries cost 3 times as much as cherries.Which equation represents the cost (y) of buying (x) pounds of strawberries?

Solution
For this case we have the following info:
Cherries (x) 3 6 9
Cost (y) 9 18 27
For this case we can solve the relation with:
y= kx
And solving for k we got:
k= y/x = 9/3 =3
Then the equation is:
y= 3x