Heidi T. answered 08/30/19
MS in Mathematics, PhD in Physics, 7+ years teaching experience
the word "difference" implies subtraction. The "and" separates the two quantities under consideration. The word "times" indicates multiplication.
So, another way to write the same thing is "multiply 7 and y, then subtract 1"
7y - 1
One thing I always recommend is that you make a "Math - English Dictionary" that has the math symbol, examples of how it is used, and all the words in English that mean use the operation.