If I understand your question well, I suppose you mean

Answer:
Gabby received
7 nickels
10 dimes
3 quarters
Step-by-step explanation:
Let
x----> the number of dimes
y----> the number of nickels
z---> the number of quarters
Remember that
1 dime=$0.10
1 nickel=$0.05
1 quarter=$0.25
we know that
0.10x+0.05y+0.25z=2.10 ------> equation A
x=y+3-----> equation B
z=y-4 -----> equation C
substitute equation B and equation C in equation A and solve for y
0.10(y+3)+0.05y+0.25(y-4)=2.10
0.10y+0.30+0.05y+0.25y-1=2.10
0.40y=2.10-0.30+1
0.40y=2.80
y=7 nickels
<em>Find the value of x</em>
x=y+3 -----> x=7+3=10 dimes
<em>Find the value of z</em>
z=y-4 -----> z=7-4=3 quarters
therefore
Gabby received
7 nickels
10 dimes
3 quarters
Answer:
C
Step-by-step explanation:
Using Pythagoras' identity to determine if the triangle is right
The square of the longest side should equal the sum of the squares on the other 2 sides, that is
QS² = RS² + QR² = 8² + 5² = 64 + 25 = 89 ( take the square root of both sides )
QS = 
Δ QRS is not right as QS would have to be 
Answer: the best answer is 3(-3a-1)
Step-by-step explanation: