Carter has 37 coins, all nickels and dimes in his piggy bank. the value of the coins is $3.10. how many dimes does carter have? how would you set this as a system of equations?

The answer is 
n = 37 - d
0.05n + 0.10d = 3.10
He has 25 dimes.

n - the number of nickles
d - the number of dimes

n = $0.05
d = $0.10

Carter has 37 coins: n + d = 37
The value of the coins is $3.10: 0.05n + 0.10d = 3.10

n + d = 37
0.05n + 0.10d = 3.10

n = 37 - d
0.05n + 0.10d = 3.10

0.05(37 - d) + 0.10d = 3.10
1.85 - 0.05d + 0.10d = 3.10
1.85 + 0.05d = 3.10
0.05d = 3.10 - 1.85
0.05d = 1.25
d = 1.25 : 0.05
d = 25