Calculate some expressions

Problem:



Solution:
1.)  $ \frac{256}{2^10} \times \frac{128}{2^{-18}} = 8388608 $
2.)  $ (15 \times 3^{-7}) \div (5 \times 3^2) = \frac{1}{6561} $
3.)  $ (-1.8 \times 5^2) \div (6 * 5 ^{-1}) = \frac{-75}{2} $