there is a percent formula for all of these types of percent problems.
It is : is/of = %/100
224 is what % of 640
is = 224
of = 640
% = x
now just sub
224/640 = x/100
cross multiply because this is a proportion
(640)(x) = (224)(100)
640x = 22400
x = 22400/640
x = 35......so 224 is 35% of 640
