You need to set up the proportion:
Part/Whole=Percent/100
Part - A part of the whole number (16)
Whole - The number you are trying to find and take the percentage of (x)
Percent - The percentage you are taking (40)
Plug in to the equation and you will get
16/X=40/100
Cross multiply and get 16(100) = 40x
Multiply and get:
1600 = 40x
Divide both sides by 40 and get:
40=x
16 is 40% of 40
ANSWER: 40
To check you can multiply 40(40%)
40(.4) = 16