I need to find out what is seven minus negative four
Amanda's answer is correct, but to really understand this kind of problem, think of it this way:
You have some money and you spend $4 at a store. You have $7 left in your pocket. Let's say you want to return the thing you bought for $4. Now you have $7 minus the -$4 spent. In other words, if you had not spent the $4, you would have $7 + $4 = 11.
Understanding how negative numbers work can be tricky, but it's worth really understanding why and how they work rather than just memorizing rules and formulas!