(# of pattie options) \* (# of topping options) \* (# of sauce options) \* (# of onion ring options)
Now think through each term one at a time.
The pattie can either be 1 or 2. So # of pattie options = 2.
The topping options are either 0, or the 7 single options, or the 7C2 = 21 combinations of 2, or the 7C3 combinations of 3, or ...
The short answer to that is that it's the number of subsets of a set with 7 elements, including the empty set (no topping) or the whole set (all 7 toppings).
That is, if you write the 7 toppings as a set of 7 elements, the possible options are all the subsets of that set.
Do you know how to calculate the number of subsets of a set?
Can you see now how to calculate the number of sauce options and the number of onion ring options?