We know the formula for kinetic energy is

KE = (1/2)mv^{2}.

If we know that c, the speed of light, is 3x10^{8}ms^{-1} (you will be given this value in your Data & Formula books in the exam) and the proton is traveling at 0.3c, it has a velocity of

0.3x3x10^{8} = 9x10^{7}ms^{-1}.

Therefore v^{2} will be (9x10^{7})^{2} = 8.1x10^{15}.

We know that the mass of a proton is 1.67x10^{-27}kg (again, you will be given this value in the exam).

Therefore kinetic energy in Joules (the SI unit, because we have currently only used SI units) is (1/2) x 1.67x10^{-27} x 8.1x10^{15} = 6.76x10^{-12}J

It is known that 1eV (electron volt) is equal to 1.6x10^{-19}J. Therefore dividing our energy in Joules by this value will give us our energy in eV.

(6.76x10^{-12}) / (1.6x10^{-19}) = 4.23x10^{7}eV.

As 1 MeV = 1x10^{6}eV, we can find our value in MeV by dividing it by 1x10^{6};

(4.23x10^{7}) / (1x10^{6}) = 42.3MeV.

This is a standard unit used in particle energies, and is quite a common question in any A Level physics exam.