Well his salary is $40,000 dollars.
$72,750 - $40,000 = $32,750
This means that 5% of the value of investments he had sold was equal to $32,750.
[tex]\frac { 1 }{ 20 } \times I=32750\\ \\ 20\times \frac { 1 }{ 20 } \times I=20\times 32750\\ \\ \therefore \quad I=655000[/tex]
The stockbroker sold $655,000 worth of investments.