20. An accountant earns $90 for preparing an individual tax return and $175 for preparing a commercial tax return. On average, an individual return requires three hours of the accountant's time and one hour of working on the computer. Each commercial return requires four hours of accountant's time and two hours working on the computer. If the accountant's time is limited to 120 hours and the available computer time is limited to 50 hours, how should the accountant divide his time between individual and commercial returns to maximize his income? What is his maximum income