JAMB Economics 2015 Paper

The formula to calculate the components of GNP is Y = C + I + G + X + Z.
That stands for GNP = Consumption + Investment + Government + X (net exports, or imports minus exports) + Z (net income earned by domestic residents from overseas investments - net income earned by foreign residents from domestic investments.)

20000 + 60000 + 10000 - 15000 = 75000