Let
n-------> the number of nickels
q------> the number of quarters
we know that

so
----> equation A
----> equation B
substitute equation B in equation A
![0.05n+0.25[3n]=1.60](https://tex.z-dn.net/?f=0.05n%2B0.25%5B3n%5D%3D1.60)



Find the value of q

therefore
<u>The answer part a) is</u>
the number of nickels are
and the number of quarters are 
<u>the answer Part b) is</u>
The expressions that represents the number of quarters is
since this a 45 45 90 right triangle to get the side lengths you divide 2 times the square root of 2 and you get 2, since this has two congruent angles which makes it an Isosceles triangle. your a and b value are 2.
The standard form of a circle is:

Your center is
and your radius is 
Plug them into the equation and you get


The correct answer is D.