You will need to subtract 3x from 5x, then since there is a minus sign in front of the 7 it will count as a -7, so u add 7 cross it out and then add 7 to the -4(which is also negative cause it has a minus sign in front) and then you have ur answer
5x-3x=2x
7+ -4= 3
Answer: 2x-3
