The answer and how to do it.

let x = orginal price of the shorts

$21 = x(100%-20%) * 1.05

$21 = x(80%) * 1.05

$21 = 0.8x * 1.05

Subtract 1.05 from both sides

$19.95 = 0.8x

Divide 0.8 from both sides

$24.9375 = x

So the orginal price of the shorts are about $24.94

the answer is 62.8 cubic units

hello from mrbilldoesmath!

answer:

(7 x + 6 y) (49 x^2 - 42 x y + 36 y^2)

discussion:

the trick is to recognize that 343 = 7^3 and 216 = 6^3 and, in general,

a^3 + b^3 =   (a + b) (a^2 - a b + b^2).

in our case

343x^3+216y^3   =   (7x)^3 + (6y)^3

so take a = 7x and b = 6y in the above equation to get the answer.

you,

mrb