Question

9 + (8 + 1) = (9 + 8) + 1

Answer 1

This is known as the associative property of addition in arithmetic.

Where a + (b+c) = (a+b) + c
:D

Answer 2

9 + (8 +1) = (9+8) +1
9 + (9) = (17) +1
18=18

Answer 3

jut remember PEMDAS
parenthesis, exponents, multiply, divide, add, subtract.