Question 17294
There are 2 equations in this problem. 
Let d= dimes
Let n= nickels
d+n=60
0.1d+0.05n=4
Use substitution to solve
n=60-d
0.1d+0.05(60-d)=4
0.1d+3-0.05d=4
0.05d=1
d=20
Now substitute d into one of the original equations
20+n=60
n=40
The girl has 20 dimes and 40 nickels