Answer:
10w^2 + 24w + 13
Step-by-step explanation:
use Foil method
we know that in direct variation as x increase y also increases.
in indirect variation x decreases y increase and vice versa.
in part a we have x at top (numerator ) and y at denominator it mean indirect variation (as x increases y decreases).
to find k we know that for indirect variation xy=k
if we rewrite the equation x=9/y we get xy=9
which mean k=9 .
in part b we have 4xy=20 if we simplify this equation we get

so here if we rewrite in terms of x.
we get x=5/y which represents indirect variation.
and we know xy=k
we have xy=5 .so k=5
40*1.2=48
1 represent the entire amount and .2 represents the tax added. When multiplied it would give you 48 as the final price.
25% 6 divided by 24 will give you the percentage of copper in the bar