Answer:

Step-by-step explanation:
when the exponent is equal, we can put the x and y together in a bracket and a as the Exponent of xy.
Hope I get your question~
60% decrease.
$105-$42 = $63
$63/$105 = 0.6
0.6 x 100 = 60
-2x^4 + 10x^3 - 21x^2 + 19x - 4
that should be the right answer