let

x = number of nickles

y = the number of dimes

z = number of quarters

1 nickle = $0.05

1 dime = $0.1

1 quarter = $0.25

a seller of fine jewelry has $8.80 in nickels, dimes, and quarters at the end of the day

0.05*x + 0.1*y + 0.25*z = 8.80

there are two times as many dimes as quarters

y = 2z

16 more nickels than quarters

x = z + 16

by solving the system of equations

0.05*x + 0.1*y + 0.25*z = 8.80

y = 2z

x = z + 16

we find

x = 32 nickles

y = 32 dimes

z = 16 quarters

the seller has 32 nickles, 32 dimes and 16 quarters.