Well that's easy it basically tells you all you gotta do is plug in the numbers
"E" is what you're trying to find out so you don't know that one it stays the same.
"S" is the amount of money she started with and it says she started with $500
And then she has $274 less than she started with.
E = 500 - 274
E= 226
She is left with $226 after her weekend at the beach.
~Hope it helped~