They use a hygrometer. It measures relative humidity (the amount of moisture in the air) A psychrometer is an example of a hydrometer
D = m/V
m = 75g
V = 4 x 4 x 4 = 64 cm^3
d = 75/64 = 1 11/64 g/cm^3
What happens is that the RNA<span> is synthesized from the template and RNA polymerase moves along the DNA, elongating the RNA transcript molecule; an enzyme forms the hydrogen bonds between the bases of the DNA strand and the complementary bases of the RNA molecule found in the nucleus.</span>
<span>Hope this helped !!</span>