Process costing joint products

Two joint products A and B are produced in a process. Data for the last period are as follows: product A sales 480 tonnes production 600tonnes, product B sales 320 tonnes production 400 tonnes. Common production costs in the period were 12000 there was no opening inventory. Both products had s gross profit margin of 40%.commoncosts were apportioned on physical basis. What was the gross profit for product A in the period?…. I managed to calculate the apportioned production costs for A and got $7200,then got a portion that attributed to the value of sales $5760 then used the profit margin 40%*$5760 and got $2304 bt the answer on the script is saying profit should br calculated as $5760*40/60. Why dividing bt 60 instead of 100 sir!