Let the total copies of Magazine X = m
Total sold at full price = 40% of m
Target question: What was the total number of copies of the magazine sold last week?

Statement 1: Last week, the full price for a copy of Magazine X was $1.50 and the total revenue from full-price sales was $112,500
1 full price magazine = $1.5
Total revenue from 40% of m = $112500
Total copies sold at full price = 112500/1.5 = 75000
Therefore, if 40% = 75000 then,
$$60\%=\frac{60\%\cdot75000}{40}=112500$$
Total copies = 112500 + 75000 = 187,500, hence, statement 1 is SUFFICIENT.

Statement 2: The total number of copies of Magazine X sold last week at full price was $75000.
Therefore, if 40% = 75000 then,
$$60\%=\frac{60\%\cdot75000}{40}=112500$$
Total copies = 112500 + 75000 = 187,500, hence, statement 2 is also SUFFICIENT.

Therefore, since statement is sufficient alone, option D is correct.