Answer:
Selenium dichloride
Explanation:
Selenium (Se) and Chlorine (Cl) are both elements capable of combining together to form a compound with the chemical formula; SeCl2. Since the chlorine atom is more electronegative than selenium atom, the chlorine pulls more electrons towards itself to form an IONIC bond.
The SeCl2 compound formed is called Selenium dichloride as two atoms of Chlorine are needed to combine with one atom of Selenium to form the compound.
It makes calculations with very large and small numbers easier.
Scientific notation is a system used in order to It makes calculations with very large and small numbers easier. It is useful as it allows very large number that would take a lot of space to write otherwise, and it allows them to be calculated easier. 
for example is a incredible large number, but written in this form is immediately understandable and useful for calculation.
Answer:
342,000kg
Explanation:
p=mv
8.55*10^7 kg*m/s=m(900 km/h)
85,500,000 kg*m/s=m(900 km/h)
(85,500,000 kg*m/s)/(900 km/h)=m
Get same units.... 900km/h = 250m/s
m/s cancel in the division, you are left with just kg!!
85,500,000/250=342,000kg! That's it!
Upstream speed = S - 1
Downstream speed = S + 1
Average speed = total distance / total time
Average speed = (S - 1) + (S + 1) / 2
= S
S = 6 miles / 4 hours
S = 1.5 miles per hour
