If P₈ and P₉ represent the population of West African in 1978 and 1979 respectively, and given that in 1979.

D= number of deaths, B= number of births, I= number of immigrants, E= number of Emigrants. Then the size of the population in 1979 is given by

• A.P₉ = P₈ + D - B = I - E
• B.P₉ = P₈ + B - D + I - E
• C.P₉ =P₈ + B - D + E - I
• D.P₉ = B - D + I - E
• E.P₉ = P₈ + B + D + I + E