Here are some helpful word problem terms:
x= a number
times= multiplication
7 times a number= 7x
difference= subtraction
difference between 7 times a number and 5= 7x - 5
is= equal sign
ANSWER: (C) 7x - 5= 51 is the answer because 5 was not multiplied by the number (x) too.
Hope this helps! :)