Okay, so it starts off with 7 less, so we know that there's a negative 7. All that's left is the product of 5 and a NUMBER. Instead of saying number, we could put a variable, such as x. Now, we'd get a product of 5 and x minus 7. Now, product means multiplication, so you'd multiply 5 and a number(x) which would end up giving you 5x minus 7. Now add subtraction and you get;
5x-7