The rule that will be used to solve this types of questions is:
M1 * V1 = M2 * V2
From the givens we have:
M1 = 15.8 m
V1 is unknown
M2 = 0.25 m
V2 = 1000 ml
Substitute with these givens in the above equation to get V1 as follows:
15.8*V1 = 0.25*1000
V1 = 15.82278 ml
