Step-by-step explanation:
first you find the volume of a bin.
that is multiplication of 3 dimensions given.
4*4*4=64 cubic feet...
now volume of books..
0.75*0.75.0.25=0.14 cubic feet
now the number of books that will fit the bin=volume of bin/volume of books
64/0.14=455
455 books
7+7+7=21 is the same as saying 7 times 3+
=21
2(5n-2)=4(n+2)
10n-4=4n+8
6n-4=8
6n=12
n=2