To calculate percent abundance from relative abundance, multiply the relative abundance by 100%. For example, if the relative abundance is 0.34, the percent abundance is 34%.  _______________________________________________________________________________________________________________________________________________________________________________________ To calculate percent abundance from atomic mass and relative atomic mass, set one unknown to x and the other to 1-x. The first unknown can replace the x in the second unknown. Therefore if [unknown 1 = a] and [unknown 2 = b] and a(x) + b(1-x) = the relative atomic mass, then  a(x) + b - bx = relative atomic mass.    Knowing the relative atomic mass and the values of a and b, you can insert them into the equation to solve for x.    Then from there, you can solve for the unknowns. _______________________________________________________________________________________________________________________________________________________________________________________   Here is a link for a helpful video: https://youtu.be/6CfSyGd5Ry4