Solve with due regard to significant figure.
`(3.0 xx10^(-8))+ (4.5 xx 10^(-6)) = `

Explanation

`3.0 xx 10^(-8) + 4.5 xx 10^(-6) = 0.03 xx 10^(-6) + 4.5 xx 10^(-6) = 4.53 xx10^(-6)`
Here `4.5 xx 10^(-6)` has only one decimal place and `0.03 xx 10^(-6)` can have two decimal places.
This result should be rounded off to one decimal place.
`therefore (3.0 xx 10^(-8)) + (4.5 xx 10^(-6)) = 4.5 xx 10^(-6)`