Combine like terms.

7 3/4x - 5 1/20x

To combine like terms, we need to first simplify the coefficients (the numbers in front of the variables) and then combine the constants (the numbers without variables).

Here's how we can simplify the coefficients:

7 3/4x can be written as (7 + 3/4)x.
To add 7 and 3/4, we need to find a common denominator, which is 4 in this case. We'll multiply 7 by 4 to get 28 and add that to the numerator of 3/4, giving us 31/4.

So, 7 3/4x simplifies to (31/4)x.

Similarly, 5 1/20x can be written as (5 + 1/20)x.
To add 5 and 1/20, we'll multiply 5 by 20 to get 100 and add that to the numerator of 1/20, giving us 101/20.

So, 5 1/20x simplifies to (101/20)x.

Now that we have simplified the coefficients, we can combine the like terms by adding the coefficients together:

(31/4)x - (101/20)x.

To combine the two terms, we need a common denominator for 4 and 20, which is 20.

Multiplying (31/4)x by 5/5 gives us (155/20)x, and multiplying (101/20)x by 1 gives us (101/20)x.

Now we can add the coefficients: (155/20)x - (101/20)x.

Subtracting the coefficients gives us (155/20 - 101/20)x.

Simplifying the coefficients gives us (54/20)x, which further simplifies to (27/10)x.

Therefore, the combined expression for 7 3/4x - 5 1/20x is (27/10)x.