(4x10^-5) + (3x10^-5) would equal .00004 + .00003 = .00007
The way to convert scientific notation to standard notation is simple:
with negative powers, simply treat it as a whole number, subtract 1 from it and add that many zeros before the number you are multiplying by 10
with positive powers, simply subtract 1 from it and add that many zeros after the number you are multiplying by 10
