Wavelength of an accelerated electron

QUESTION: Approximately what is the "de Broglie" wavelength of an electron that has been accelerated through a potential difference of = 150 V? (The mass of an electron = 9.11 x 10^-31 kg.)
Possible answers:
(a) 0.1 nm
(b) 1 nm
(c) 10 nm
(d) 100 nm
(e) 1000 nm

Answer:

The kinetic energy of an electron accelerated through a potential difference of V volts is given by the equation:

½ mv² = eV where e is the electron charge (1.6x10^-19 C) [You must be given the electron charge and Planck's constant in order to answer this question].

and so v = square root (2eV/m) = 7.26x10⁶ m/s

Therefore: wavelength = h/mv = h/[9.11x10^{- 31}x7.26x10⁶] = 1x10^-10 = 0.1 nm

The correct answer is (a)