If the combined GDP of the six countries has grown by 50% in the last decade, then what was their combined annual Gross Domestic Product (in billion USD) before 10 years?

Let the combined annual Gross Domestic Product (in billion USD) before 10 years = $$100x$$

It is grown by 50%, => Combined GDP in 2016 (in billion USD) = $$\frac{150}{100}\times100x=150x$$

Combined GDP of the six countries (in billion USD) in 2016 :

= 30 + 100 + 70 + 20 + 90 + 50 = 360

According to ques,

=> $$150x=360$$

=> $$x=\frac{36}{15}=2.4$$

$$\therefore$$ The combined annual Gross Domestic Product (in billion USD) before 10 years = $$100\times2.4=240$$

=> Ans - (C)