$3\mathrm{.}16($Gas Mileage$)$ Drivers are concerned with the mileage obtained by their automobiles. One

driver has kept track of several tankfuls of gasoline by recording miles driven and gallons used for

each tankful$.$ Develop a program that will input the miles driven and gallons used for each tankful$.$

The program should calculate and display the miles per gallon obtained for each tankful$.$ After pro$-$

cessing all input information, the program should calculate and print the combined miles per gallon

obtained for all tankfuls$.$ Here is a sample input$/$output dialog:

Enter the gallons used $(-1$ to end$)$: $12\mathrm{.}8$

Enter the miles driven: $287$

The miles$/$gallon for this tank was $22\mathrm{.}421875$

Enter the gallons used $(-1$ to end$)$: $10\mathrm{.}3$

Enter the miles driven: $200$

The miles$/$gallon for this tank was $19\mathrm{.}417475$

Enter the gallons used $(-1$ to end$)$: $5$

Enter the miles driven: $120$

The miles$/$gallon for this tank was $24\mathrm{.}000000$

Enter the gallons used $(-1$ to end$)$: $-1$

The overal$1$ average miles$/$gal$1$on was $21\mathrm{.}60142\backslash$