If you would like to know how long would it take John to mow the lawn alone, you can calculate this using the following steps:
hours (Jessica) ... a
hours (John) ... b = ?
a + b = 11
b = 4 * a
___________
a + b = 11
a + 4 * a = 11
5 * a = 11 /5
a = 11/5 = 2 1/5 = 2.2 hours
b = 4 * a = 4 * 2.2 = 8.8 hours
The correct result would be 8.8 hours.
