Let's say Jason invested x amount of money.
Since Jason started investing, he has earned the same amount he invested twice over in 5 months, meaning he has earned x+2*x=$90
This evaluates to 3x=$90
The total amount of money that Jason invested is x=$90/3
Jason invested x=$30
The total amount of money that Jason has earned from his investments is $90-$30=$<<90-30=60>>60
If he earned an equal amount of money from the investment in five months, his monthly returns is 60/5=$<<60/5=12>>12
#### 12