The monthly profit for the merchant increases by Rp. 18,000. So, to find the total profit until the 12th month, we need to calculate the sum of an arithmetic series. The formula for the sum of an arithmetic series is Sn = (n/2)(a + l), where Sn is the sum of the series, n is the number of terms, a is the first term, and l is the last term. In this case, n = 12, a = Rp. 46,000, and l = Rp. 46,000 + (12-1) * Rp. 18,000 = Rp. 46,000 + Rp. 198,000 = Rp. 244,000. Plugging in these values into the formula, we get Sn = (12/2)(Rp. 46,000 + Rp. 244,000) = 6 * Rp. 290,000 = Rp. 1,740,000. Therefore, the correct answer is A. Rp. 1,740,000.