This is because there are three consecutive 4s, so you have to put the 4 into exponential form 3 times. So the exponential form for the 4s will be 4³. There are also 2 consecutive 5s so you have to include 2 in the exponential form. So, the exponential form of the 5s is 5². Now you have to somehow multiply them together. You could do this by putting a multiplication sign, (4³×5²) or you could bunch them together and it will mean the same thing (4³5²).
