80,000,000 = 80,000,000 (in expanded form)
80,000,000 = eighty million (in word form)
80,000,000 = 8 x 10^7 (in standard form)
The answer to your question is 2
B.) Marua will spend 2 hours to read 100 pages of sociology which means she can only read 60 pages of economics.
Therefore, the opportunity cost of reading 100 pages of sociology is forfeiting 40 pages (2 hours) of economics.