Which is a graph of f(x)=4(1/2)x

We know that the basic equation of exponential equation equation is; 

y=ab^x 

Where a is the y-intercept/starting point and b is the value that x exponentially grows or decays. 

From the given equation, the two graphs with other intercepts (not 4) can be removed. 

Since b is between 0 and one, this function should be decaying. 

Next calculate the value of x when y=1. 

1=4(0.5)^x 
1/4=(1/2)^x 
log₀₋₅(1/4)=x 
2=x

Check which of the graphs have y=1, x=2. This would be the second graph, which would represent the equation y=4(0.5)^x 

Hope I helped :)