Isotones contain same number of neutrons and different number of protons.
179C and 8B are isotones.
They contain 17−9=8 neutrons.
Hence, mass number of B is 8+8=16
Isobars have same mass number but different atomic number.
168B and 7A are isobars.
The mass number of A will be same as that of B i.e, 16.
The number of neutrons in A =16−7=9