The answer is "Math".....but technically the official name for it is Mathematics.
It’s literally 3a plus 87 if you’re asking 3a plus 8 times 7 then it’s 3a plus 56
Okay so you are going to really just add 30 + 9 here and that means you have 30 tens and 9 ones or a 30 in the tens place and a 9 in the ones place.
I hope i broke that down well enough.
I hope this helped :)
