Question

(7.2x10^-6)+(5.44x10^-6)

Answer 1

(7.2x10^-6)+(5.44x10^-6)
Line up the decimal point, then add.
0.0000072
+0.00000544
--------------------
0.00001264
Have you talked about significant figures? When adding numbers, the answer may not more significant figures to the right of the decimal than the LEAST figure in any of the numbers being added. So the last 4 is dropped and the answer is 0.0000126
Or you can do it another way.
7.2E-6
+5.44E-6
-------------
12.64E-6 = 1.264E-5. Then we drop the last 4 as above to read 1.26E-5