16. Party A excavates a canal, on the first day digging $\frac{1}{4}$ of the total length of the canal, on the second day digging $\frac{5}{21}$ of the remaining length, on the third day digging $\frac{1}{2}$ of the remaining length, and on the fourth day finishing the remaining 100 meters of the canal. Therefore, the length of the canal is $\qquad$ meters.