EXPLANATION :
From the problem, Joey had d one-dollar bills and f five-dollar bills.
The total amount in his wallet will be :
[tex]\begin{gathered} Amount=\$1\times(d)+\$5\times(f) \\ Amount=d+5f \end{gathered}[/tex]
When d = 7 and f = 4, the total amount in his wallet is :
[tex]\begin{gathered} Amount=d+5f \\ =7+5(4) \\ =27 \end{gathered}[/tex]
ANSWER :
The expression is Amount = d + 5f
The amount in his wallet is $27
