The correct quantifier in this context is "many".
The word "many" is used with countable plural nouns such as "millions". Since "millions" is countable, "many" is the appropriate choice.
The sentence becomes:
Brazil earns many millions of pounds a year from coffee exports.
The correct sentence is "Brazil earns many millions of pounds a year from coffee exports."
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?