answer is (a)
Step-by-step explanation:
first thing we should find the equation which is f(X)=a*b^x
so the always will be the y intercept no matter what
now time to find b if graph that is shown start from 1 until the end of line which is in the graph so you will find it 8 now divide 8 by 4 so 8/4=2
so final equation will be f(x)=2*(4)
i hope i helped out