Haven't read all the previous pages but when solving an equation
one uses BODMAS.
This is an acronym for
B.......Brackets
O.......Of
D.......Division
M.......Minus
A.......​Addition
S.......Subtraction

So, first the Brackets..1+2=3
now we have 6/2x3
now the "of" which is 2x3=6
now we have 6/6
Do the Division and 6 divided by 6=1
Q.E.D.