We are given a problem that can be solved by a system of equations. Let N be the number of nickels, D the number of dimes, and Q the number of Quarters. Since in total he has 4.2, this means mathematically:
![N+D+Q=4.2,\text{ (1)}](https://img.qammunity.org/2023/formulas/mathematics/college/ccvf9fsa97oyvsc84y0cgy2a65cvrbop2n.png)
We are told that he has 6 more dimes than nickels, this can be written like this:
![D=6N,\text{ (2)}](https://img.qammunity.org/2023/formulas/mathematics/college/c5da8eiabs4ze9flra1z8syc3sk63scq33.png)
We are told that he has three-time Quarters than nickles, this is:
![Q=3N,\text{ (3)}](https://img.qammunity.org/2023/formulas/mathematics/college/5euztx4bypqoo92e23yt136tvi6ihypw18.png)
Now, if we replace equation (2) and (3) in equation (1), we get:
![N+6N+3N=4.2](https://img.qammunity.org/2023/formulas/mathematics/college/ockqfybpt2ytoo03jtf0nckbb8yb6dfiol.png)
Solving for N, we get;
![\begin{gathered} 10N=4.2 \\ N=(4.2)/(10)=0.42 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/2memnjh1qwc4f041858b7cghmgg9yjqigk.png)
Replacing the value of N in equation (2), we get:
![\begin{gathered} D=6N \\ D=6(0.42)=2.52 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/tryp2kqo1meard4ya6qat6nmx90voroo9b.png)
Now we replace the value of N in equation (3):
![\begin{gathered} Q=3N \\ Q=3(0.42)=1.26 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/tmay31sa48lnr71swq6ekrz63hbqi9uphh.png)
Therefore, he has, 0.42 in nickels, 2.52 in dimes, and 1.26 in quarters.