You can only add or subtract numbers in scientific notation if they have
the same power of 10. If they're different, then you have to change one
to match the other one.
Here are both ways to do your example:
3.72x 10^9 = 37.2x10^8
(37.2 x 10^8)+(5.46 x 10^8) = (37.2+5.46) x 10^8 = 42.66x10^8 = <em>4.266x10^9</em>
=======================
5.46 x 10^8 = 0.546 x 10^9
3.72 x 10^9 + 0.546 x 10^9 = (3.72 + 0.546) x 10^9 = <em>4.266 x 10^9</em>
Answer:
= 15 m/s
Explanation:
Considering right side(west) as positive x-axis and south as negative y-axis.
velocity of boat in still water 
velocity of stream 
now relative velocity of boat w.r.t. stream 
this velocity with which ac distance will be covered.
therefore magnitude of 
= 15 m/s