In a pack of construction paper, the numbers of blue and red sheets are originally in the ratio 2:7. Each day, Laura uses 1 blue sheet and 3 red sheets. One day, she uses 3 red sheets and the last blue sheet, leaving her with 15 red sheets. How many sheets of construction paper were in the pack originally?
(A) 144
(B) 252
(C) 135
(D) 270
(E) 105
Suppose that Laura uses the last blue sheet on day number $d$.

Then the total number of blue sheets with which she started was $d$.

Since she uses 3 red sheets per day and has 15 red sheets left over, then she started with $3 d+15$ red sheets.

Since the blue and red sheets were initially in the ratio $2: 7$, then

$$
\begin{aligned}
\frac{d}{3 d+15} & =\frac{2}{7} \\
7 d & =6 d+30 \\
d & =30
\end{aligned}
$$

Thus, she started with 30 blue sheets and 105 red sheets, or 135 sheets of construction paper in total.

Answer: (C)