The product of 2 and the difference of a number and 3.​
Here, we want the PRODUCT of something and something...
What thing?
Check the sentence, we want product of:
"2"
and
"difference of a number and 3"
The 2nd part is itself making another expression. Thus, "difference of a number (call it x) and 3 can be written as:
x - 3
Now, going back:
we want product of "2" and "x - 3", we ccan write:

This would be the unsimplified expression.