Easy
nPr=

here
36P19=



1045843337171591729971200000
Commutative property is one of the basic properties of numbers. Numbers can be added or multiplied in any order because changing the order of the number doesn't change the sum or the product.
Part=percentage*whole
50=0.40w
Divide each sde by 0.40 and you get 125. 50 is 40% of 125.
A
(X-7)(x-4) -> x^2 -11x + 28
Multiply that by the 2 and you get the original equation!