If you know the length and width of a rectangle ,you can work out the perimeter of the whole rectangle .explain how.

MULTIPLY LENGTH TIMES WIDTH. EXAMPLE. 7 = LENGTH AND WIDTH EQUALS 4   7 TIMES 4 = THE PERIMETER OR IN OTHER WORDS 28

Simply: Perimeter=width+width+length+length; you just add evry side of the rectangle 

You multiply the percent by 100 which should make it a decimal, for example,

20% • 56 = x

First you have to make 20% (example) a decimal, the rule is that you must multiply the percent always by 100 not 10 but 100
20% to a decimal is 0.2
Since you know what 20% is as a decimal,
You now can multiply 56 (example) and 0.2 (example) which brings you to

That should answer your question