Question 905323
Remember that there are two ways to tell whether a graph is an example of exponential decay or exponential growth.

 A graph that is decreasing or showing exponential decay :

   y= ab^x
where a > 0 and b is between 0 and 1 .

For example, in y= 200 ( 0.5) ^ x , each time x is increased by 1, y is decreased by 1/2 of its previous value. 

A graph that is showing increasing growth :

y= ab^x
where a >0 and b is greater than 1 , the graph will be increasing.

For this example, we have 3(0.25)^x, and we can see that b is between 0 and 1, so that's why this is a graph of exponential decay, where each time x is increased by 1 , we see that y is decreased by 1/4 of its previous value.

y= 3(0.25)^1 = 0.75
y= 3(0.25)^2 = 0.1875 (this is 1/4 of 0.75)
y= 3(0.25)^3 = 0.046875 (this is 1/4 of 0.1875)
y= 3(0.25)^4 = 0.0117188(this is 1/4 of 0.046875)

To find the y intercept,  we would designate x=0. Why? Any y intercept, whether of a linear or exponential graph ,would always have 0 as the value of x. 

So, y= 3(0.25)^0
    y= 3 (1)
    y= 3.

Note:anything to the power of zero is always 1.