() the table below - does it represent an exponential function? x 1 2 3 4 y 4 16 64 256

Short I don't know, but that doesn't mean I can't give you something that you can decide for yourself.
y = 4*2^(2n - 2) is the pattern.
Go for broke. Try n = 4. You should get 256. Let's try it.
y = 4 * 2^(2*4 - 2)
y = 4 * 2^(8 - 2)
y = 4 * 2^6
y = 4 * 64
y = 256 yup it works.

The other end is just as important. Suppose n = 1
Then y = 4 * 2^(2*1 - 2) = 4 * 2^0 = 4*1 = 4 Both work.

If this formula is correct, we can abbreviate it to make your task easier.
y = 4 * 2^(2n - 2)
y = 2^2 * 2^(2n - 2)
y = 2^(2n - 2 + 2)
y = 2^(2n) Now try the two end points again.

n = 4
y = 2^(2*4)
y  =  2^8
y = 256

n = 1
y = 2^(2*1)
y = 2^2
y = 4 which again checks.

so y = 2^(2n) I think is an exponential function.
Sorry my explanation is so long.