to answer this you would add the amout of pages left to read with the amount of pages she has already read.
if she read 16 pages then there would be 200 pages in total.
dc=6 square root of 3 and ac is 12 square root 3
c and d
square root of 3/2 = 18/c
cross multiply to get 18*2=√3*c
36/√3 * √3/√3 = c
answer is the third choice: