(a).Add `3.8 xx 10^(-6) to 4.2 xx 10^(-5)` with due regard to significant figures.
(b). Subtract `3.2 xx 10^(-6) from 4.7 xx 10^(-4)` with regard to significant figures.
( c ). Subtract `1.5 xx 10^(3) from 4.8 xx 10^(4)` with due regard to significant figures.