We know that when we dilute a solution the number of moles remains the same just the concentration changes [moles per unit volume]
So we can equate the moles before dilution and after dilution
moles = molarity X volume
a) Initial moles = final moles [NaOH]
M1= initial molarity = 0.240 M
V1= initial volume = 78 mL
M2= final molarity = ?
V2 = final volume = 0.250 L = 250mL
therefore
final molarity = 0.075 M
b)
Initial moles = final moles [Nitric acid]
M1= initial molarity = 1.20 M
V1= initial volume = 38.5 mL
M2= final molarity = ?
V2 = final volume = 0.130 L = 130mL
therefore
final molarity = 0.355 M