Which level of organization is characterized by a group of cells that work together to perform a common function? i need help with this question

Organization in organisms is like this:

cells => tissues => organs => organ systems => organisms

Since we are talking about a group of cells, this would be a tissue. Don't let the word 'function' confuse you. Tissues do functions as well as an entire organ or organ system.

It is helpful to use the flow chart when asked questions like these, so make sure to memorize it! It will be helpful in any level of science.

I hope this helps!

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.