Luke runs a farm stand that sells strawberries and blueberries. Each pound of
strawberries sells for $3 and each pound of blueberries sells for $4. How much would
Luke make if he sold 12 pounds of strawberries and 49 pounds of blueberries? How
much would Luke make if he sold s pounds of strawberries and b pounds of
blueberries?

He would make $36 for 12 pounds of strawberries
He would make $196 for 49 pounds of blueberries

He would make 3S if he sold S pounds of strawberries
He would make 4B if he sold B pounds of blueberries

Working:
We know that strawberries are $3/pound so $3 x 12pounds = $36
We know that blueberries are $4/pound so $4 x 49pounds = $196

The letters represent the amount of pounds of fruit being bought so the calculation for that is ($ x pounds) so you would write this but without assigning a numerical value to the amount. So if the strawberries are $3/pound and Luke sold ‘s’ pounds then it would be 3S (or 3xS but that is already assumed). The same goes for the blueberries. We know that they are $4/pound so it would be 4B.

Sorry if this doesn’t make any sense but I hope this helped