Simplify without a calculator. Give the answer without scientific notation.

a) [[$ \displaystyle\frac {4 \cdot 10^{23}} {2 \cdot 10^{19}} = $]]

b) [[$ \displaystyle\frac {-10^{25}} {-2 \cdot 10^{21}} = $]]

c) [[$ \displaystyle\frac {5 \cdot 10^{7}} {(-1 \cdot 10)^{4}} = $]]

d) [[$ \displaystyle\frac {2 \cdot 10^{6}} {-10^{1}} = $]]