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.)  $(-1.8 \times 5^2) \div (6 * 5 ^{-1}) = \frac{-75}{2}$