Answer :
.4 M means that in 1 Liter of solution there are .4 moles.
Molarity x Liters = Moles
We have molarity, so convert mL to liters
250 mL x 1000mL/1 Liter = .25 L
Now, set up the equation
.4 M x .25 L = .1 moles of solute
Molarity x Liters = Moles
We have molarity, so convert mL to liters
250 mL x 1000mL/1 Liter = .25 L
Now, set up the equation
.4 M x .25 L = .1 moles of solute