It sounds like initially we have a total of 18*5 = 90. Then we are adding 5 + 4 +3 +2 +1 to this.
so that gives us 105.
105/5 = 21
Answer:
C I think. Sorry if it's incorrect but I pretty sure it isn't.
One may note you never quite asked anything, now, assuming simplification,
Send a picture of it ok then i answer