Answer:
or
.
Step-by-step explanation:
We have been given that Nigel is planning his training schedule for a marathon over a 4-day period. He is uncertain how many miles he will run on two days. One expression for the total miles he will run is
.
The Commutative Property of Addition states that we can add numbers in any order. For example a and b be two numbers.
According to Commutative Property of Addition
.
Similarly, we can write an equivalent expression to our given expression as:

We can simplify our expression as:
.
Therefore, our required expression would be
or
.