Total number of stocks bought = 20
Rate at which each stocks were bought = 31 1/2
= 63/2
Rate at which 20 stocks were bought = 20 * (63/2) dollars
= 10 * 63 dollars
= 630 dollars
Rate at which each stocks were sold = 35 1/4
= 141/4 dollars
Rate at which 20 stocks were sold = 20 * (141/4) dollars
= 5 * 141 dollars
= 705 dollars
705- 630====== 75 C you made a profit of $75.00