What value is missing from this table

The missing value in the table is:

                  B.     15.75

The table is given by:

Gallons of gas              Cost in dollars

       1                                1.05

       2                                2.10

       5                                5.25

       15                                ?

       20                              21.00

Let x represents the Gallons of gas

and y represents the cost in dollars.

By looking at the table we observe that the relationship between x and y is linear and the equation that satisfies the equation is:

Hence, when x=15 we have:

Hence, the correct answer is:

                 Option: B