A nickel is equivalent to 0.05 dollars while a penny is equivalent to 0.01 dollars.
a) Therefore if D is the total number of dollars,
[tex]\begin{gathered} D=0.05\cdot70+0.01\cdot100=3.5+1=4.5 \\ \Rightarrow D=4.5 \end{gathered}[/tex]Therefore, the answer to the first question is 4.5 dollars.
b) Similarly, if one has x nickels and y pennies,
[tex]D=0.05x+0.01y[/tex]The answer to the second question is 0.05x+0.01y
