Lets see
a and b are legs
c=hypotnuse
a^2+b^2=c^2
10^2+b^2=10^2
100+b^2=100
minus 100 both sides
b^2=0
b=0
false, if you have a leg legnth 0, then they lines are right on top of each other
no cannot
There's only information to answer question C.
We can only know that 32 marbles were chosen. (yellow and black)
Why?
To answer the first two questions (a and b), we need to know the total number of marbles, so, we can only answer the last question (c).
We know that 7/10 of the 20 yellow marbles were chosen.
So, calculating we have:

Also, we know that 18 black marbles were chosen, so, the total of marbles chosen is equal to 32 (yellow marbles and black marbles)

Have a nice day!
I'd suggest you begin by subtracting 4 / (x-4) from both sides. Doing that would leave you with 1 / (x-4) - 2 / (x+2) = 0.
LCD is (x-4)(x+2). Mult. all three terms by (x-4)(x+2). The resulting equation is
x+2 - 2(x-4) = 0. Then x+2 = 2x - 8 => x = 10
Subst. 10 for x in the original equation to verify that 10 is indeed a solution.
First blank is 60 second blank is 12 third blank is 2
The value of new will be 8. Hope I'd help you out there.