science
posted by David .
Which shows the expression below simplified?
(3.6 × 10^15) + (1.8 × 10^12)
a. 3.60018 × 10^15
b. 3.902 × 10^14
c. 3.618 × 10^15
d. 3.6018 × 10^15

To the correct significant digits, none of the answers. For the life of me, I don't understand your teacher on this.
change both to the same power:
3.6E15=3600E12 Now add, or 3601.8E12
or 3.6018E15.
However, using scientific notation,
3.6E15 is not 3600E12 because of the zeroes being added. Only significant digits can be displayed in the digits portion. 
????? Please help

35m=_________km

scientific notation
78,990 
D is the correct answer. Convert to 10^15 and then add. Significant digits for addition key on the decimal point location, so 3.6018 x 10^15 is correct.