(Significant Figures) I am doing it right, but it says I'm wrong? Please help

1) Add (9.9x10^3s) + (9.7x10^4s) +(0.019x10^6s)

I got 125900 but it says I am wrong? I guess it has something to do with significant figures...

2) Express the following sum with the correct number of significant figures: 1.50m +154.3 cm+ 5.38x10^5 nanometers

how many meters is this?

I converted everything to meters: 1.50+ 1.543+ 5.38x10^-4 = 3.043538 but it still says I'm wrong. Significant figures again.

Thanks for any help!

1) 9900s+97000s+19000s = 125900s. now move the point to the left it becomes 1.259x10^-5s ok now u should know the rules of add significant figures. now we round off the digits
1.26x10^-5
1.3x10^-5 this is the ans
2) this will be also same way after getting answer u should get round off ans will ne 3.044 or 3.0435

The first one only has 2 significant digits. I'm not going to check the math, but the whole idea behind scientific notation is to indicate the number of sig digs. All of these have 2. So the answer is 130000.

Your next one is 3 significant digits. The nanometers won't effect anything, so you need not think about them. Your answer is 3.04 m.

For question 1 the answer may be expected in significant figure format - 125900 looks correct. try it as 1.259 times 10 to the power 5.