Which graph best represents the function f(x)=4(1.5)x?

Assuming the function is  f(x)=4(1.5)^x, the answer is the second graph.

Both of the graph looks like a^x graph but you seem to put the function incorrectly. If the function is  f(x)=4(1.5)^x, the value when x=0 would be:

 f(x)=4(1.5)^x
 f(0)=4(1.5)^0
 f(0)=4*1= 4

The y-intercept should be 4