Ireally do not know how to do this, i already asked my teacher to explain it to me, but i still don’t understand. can someone me i would be very grateful.

1. to calculate molar mass , you need average atomic mass of each element.

formula is simple

suppose we have Na2CO3

here it says

there are

2 atoms of Na

1 atom of C

3 atom of O

now

molar mass = (total atoms of Na × average atomic mass of Na) + ( total atom of C × average atomic mass of C )+ (total atom of O × average atomic mass of O)

i hope you can figure out it now.

in case of (NH4)2

this means you have 2 count of NH4

so total atoms of N = 2

total atoms of H = 4×2 = 8

so on you can now figure it out

2. balanced equation

here LHS and RHS shoild have same number of atoms of each element .

for example

H2 + Cl2 => 2HCl

here 2 atoms of H combined with 2 atoms of Cl , we know H and Cl combined and formed HCl now because total H atoms are 2 and Cl atoms are 2 in LHS then we should also have 2 atoms of each in right side

so thats why we have 2HCl in right side.

Try to figure out . let me know if need any help