Question

One hundred times the quantity seven plus two

Answer 1

"seven" means ' 7 '

"two" means ' 2 '

"the quantity seven plus two" means  ' (7 + 2) '

"one hundred times the quantity ..." means  ' 100 (7 + 2) ' 
That's the expression.

One of the rules for handling these things is that you should always
take care of anything inside parentheses first.  So do that.

         (7 + 2)  =  9

Now you can can write the expression like this:    ' 100 (9) ' .

That's just  900 .