C) (0.85 + x/100)(250+145) does not give the correct answer.
Explanation A) works; adding the two costs together is 250+145=395. We multiply this by 0.85 because 100%-15%=85%=0.85. We also have x% tax, which is represented by x/100, added to 100% of the value, or 1.00. Altogether this gives us 395(0.85)(1+x/100) = 395(0.85 + (0.85x/100)) = 395(0.85) + 395(0.85x/100) = 395(0.85) + 395(0.0085x) B) works; we have 250+145 for the original price; we have 85% = 0.85 of the value; we also have 100% + x%, which is (100+x)/100. C) does not work; (0.85+x/100)(395) does not take into consideration that you are finding the tax after taking the 85%. This will simplify out to 0.85*395 + (x/100)(395) = 335.75 + 395x/100 = 335.75 + 3.95x, which is too much. D) works; simplifying the expression from A, we have 395(0.85) + 395(0.0085x) = 335.75 + 3.3575x.
She reads at 55 pages per hour for 4 hours so 55*4 = 220 pages so far. This means that she read 220 and had 330 left so 220 + 330 = 550 so the book is 550 pages. If she reads 55 pages per hour and there is a total of 550 pages, 550/55 = 10 hours to read the book.
