Advantages of having only one si unit for pressure

The volume of helium in a blimp is 6.28 x 10^9 millimeters. the density of helium in the blimp is .1786 kilogram/meter^3. find the mass of the helium in the blimp.

Helium decays to form lithium. which equation correctly describes this decay?

How many neutrons does an element have if its atomic number is 50 and its mass number is 166