If it is an exponential function it has the form f(x) = c.ax
Now let us substitute using the values of the table.
f(-1) = c.a-1 = c/a= 1/4
f(0) = c.a0 = c = 1/2
Since any number raised to the zero we can use this to find the value of a.
Remember f(-1) = c.a-1 = 1/4
Multiply both sides by a and get
1/2 = c = a/4 so a = 4(1/2) =2
You can check to see it works for the other values in the table.
Another way to approach this is to note that the values of f(x) each time x increases by 1.
For the second question, note that shifting a function up wards by a units increases f(x) by a so it is a units higher than the original.