How many neutrons are in an atom with each set of atomic numbers and mass numbers?

Aluminum–lithium (al-li) alloys have been developed by the aircraft industry to reduce the weight and improve the performance of its aircraft. a commercial aircraft skin material having a density of 2.47 g/cm3 is desired. compute the concentration of li (in wt%) that is required.

Which is the layer underground where all empty spaces are filled with a combination of air and water ?

For ai it's atomic number is 13 and it's mass number is 27 how many neutrons does it have