set up as follows
x = nickles
y = dimes
.05(x) + .10👍 = 5.50
remove decimals
5x + 10y = 550
2nd equation
x = y + 5
because you have 5 more nickles than dimes
substitute new equation in for (x) of original equation
5 (y + 5) + 10 y = 550
5y + 25 +10y = 550
15 y = 525
y = 35
35 dimes
40 nickels
or
half of 5.50 is roughly 2.75 since you have about as many dimes as nickels
so think somewhere aound 30 dimes. This will be one where it would make more sense to solve the problem backwardss from the 4 choices they give you
especially since you're working in 10s and 5s