The y intercept of this function is always (0, a).
This is because when we place 0 in for x (which is the only way it'll be on the y-axis, we get 'a' as a result. This is because of the rule that raising anything to the 0th power will result in the number 1 and multiplying anything by 1 gives us the same number. See the work below for the example.
F(x) = a*b^x
F(0) = a*b^0
F(0) = a*1
F(0) = a
And for an example with a random number, we'll use a = 5 and b = 3
F(x) = 5*3^x
F(0) = 5*3^0
F(0) = 5*1
F(0) = 5
No matter what a and b equal, the intercept will be the a value.