5. Mining a ton of coal now generates a profit of R8,000 and mining a ton of coal next year will generate a profit of R8,400. The interest rate is 6%. The mine owner should:

(a) delay mining until next year;

(b) mine between 25% and 49% of the coal this year;

(c) mine exactly 50% of the coal this year;

(d) mine between 51% and 75% of the coal this year.

(e) mine all the coal this year.

Answer is E - can you please explain