First we find the energy level with the following formula, where a is the energy level, n1 is the final energy level, n2 is the starting energy level and r is Rydberg's constant in Joules

We insert the values


The wavelength is found with this formula, where h is Planck's constant and c is the speed of light

Finally we insert the values

Which is the same as 93.8 nm
A valve is a flap of tissue that prevents blood from flowing back
A fixed volume is where either a solid or liquid has a volume that is constant under the same pressure and temperature. A gas cannot have a fixed volume because it changes by itself without any human interaction.
Best of Luck!
Think of it like a graph. You start at the origin which is (0,0). go three to the east which now you are (3,0). Then, six to the north. Now, you are at (3,6). 1 to the east, ((4,6). Then you go 4 to the west which is back tracking. So, you end at (0,6) which is saying you are now 6 km north from your campsite.
Hope this helps!
Weight equals mass times gravitational acceleration=400N, so mass=400/9.8=41kg approx.