I'm assuming that when you wrote "(7x/2-5x+3)+(2x/2+4x-6)," you actually meant "<span>(7x^2-5x+3)+(2x^2+4x-6). Correct me if I'm wrong here.
</span><span>+(7x^2-5x+3)
</span><span>+(2x/2+4x-6)
-------------------
=9x^2 - x - 3 (answer) </span>
Let a = speed of the plane A, and b = speed of plane B.
(Assume that the net effect of the wind is negligible.)
From the first sentence, the distance between A and B after each travels for 1 hour is a + b miles. From the second sentence, after 45 minutes, or 0.75 hour, the distance between A and B is 200 miles. Plane a has traveled 0.75a, while plane B has traveled 0.75b.
Hence a + b = 0.75a + 0.75b +200
==> 0.25(a + b) = 200.
==> a + b = 800.
Therefore planes A and B are 800 miles apart now.
We want to solve 9a² = 16a for a.
Because the a is on both sides, a good strategy is to get all the a terms on one side and set it equal to zero. Then we apply the Zero Product Property (if the product is zero then so are its pieces and Factoring.
9a² = 16a
9a² - 16a = 0 <-----subtract 16a from both sides
a (9a - 16) = 0 <-----factor the common a on the left side
a = 0 OR 9a - 16 =0 <----apply Zero Product Property
Since a = 0 is already solved we work on the other equation.
9a - 16 = 0
9a = 16 <----------- add 16 to both sides
a = 16/9 <----------- divide both sides by 9
Thus a = 0 or a = 16/9
D.) the moon he wanted to go to the moon before any other countries
330cm^3 = 6cm x 5cm x L
330^3 = 30cm^2 x L
L = 11cm