If MNP is a straight line, this is simple.
Angle MNR = 78°
Angle PNV = 17°
Every angle that lies on a straight line (such as MNP) will always add up to 180°.
So to find angle RNV, we just need to add up the other angles and subtract it by 180°. This will give us the missing number that is angle RNV, which if we add with the other angles will add up to 180°.
78° + 17° = 95°
180 - 95 = 85°
Angle RNV = 85°
Double check by making sure all the angles on the line MNP adds up to 180°
RNV = 85°
Angle MNR = 78°
Angle PNV = 17°
85° + 78° = 163°
163° + 17° = 180°