A sample of Element X is found to contain 72.15% of isotope type 1 (84.91 amu) and 27.85% of isotope type 2 (86.91 amu). Calculate the average atomic mass.

Sorry i dont understand the question can you rephase it?

The correct answer is:   [a]:   "polar easterlies move cool air to the mid-latitudes."

The internal energy of the system we can term it as total potential energy and kinetic energy. energy flows out of the surrounding from the system then we can say that the internal energy of the final state is lower than its initials. the sign of  δesystem is negative.δesystem = efinal - einitial=-ve  efinal  ∠einitial.