We are given that Mary can mow a lawn in four hours and Tom can mow the lawn in five hours.
To find the fractional part of the lawn that remains to be mowed after Tom works for X hours alone, we need to determine the value of X.
We can start by finding the rate at which Tom mows the lawn.
Tom can mow the lawn in 5 hours, so his mowing rate is 1/5 of the lawn per hour.
If Tom works for X hours, he will mow a fraction of the lawn equal to (1/5) * X.
To find the fractional part that remains to be mowed, we subtract this fraction from 1 (since 1 represents the whole lawn):
Fraction remaining = 1 - (1/5) * X
Given that the fractional part remaining is 3/5, we can set up the equation:
3/5 = 1 - (1/5) * X
Multiplying both sides of the equation by 5 to eliminate the fraction, we get:
3 = 5 - X
Subtracting 5 from both sides of the equation, we find:
-2 = -X
Multiplying both sides of the equation by -1, we get:
2 = X
The value of X is 2.
The answer is: 2
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
Mary can mow a lawn in four hours and Tom can mow the lawn in 5 hours. If Tom works for X hours alone, what fractional part of the lawn remains to be mowed?
If we know the answer to the above question is \frac{3}{5}, what is the value of unknown variable X?

### Answer:
