maybe the blank is 'exponent' so
exponents tell how many times the number multiplies aginst itself
8^x^3 means (8^x) times (8^x) times (8^x)
you could fill the box with any number
if you want a power of 9 then subsitutte 9 for x
8^9^3=(8^9)^3=(134217728)^3=2417851639229258349412352
