You have a stock solution of 15.8 m nh3. how many milliliters of this solution should you dilute to make 1000.0 ml of 0.250 m nh3?

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

Idon't know hope someone you