how do you find the percentage of an element in a compound?. like for ex: H2S. what is the percent of hydrogen in that? also, how do you find the molar mass of an element?

Asap! how do you lengthen a pattern piece? (family and consumer science, sewing)

When a spring is compressed, the energy changes from kinetic to potential. which best describes what is causing this change?

One of the hopes for solving the world's energy problem is to make use of the fusion reaction 21h +31h --> 42he + 10n + energy how much energy is released when 1 mol of deuterium is fused with 1 mol of tritium according to the above reaction? the masses of the atoms and the neutrons are as follows: 21h = 2.0140 amu 31h = 3.01605 amu 42he = 4.002603 amu 10n = 1.008665 amu. the speed of light is 2.9979 x 108 m/s.