Let's have a go...
We know distance to PET = (DH)/(O+H), substituting..
(60/100)*1200 = (1200*H)/(O+H) therefore
(60/100) = H/(O+H) and, if we wanted to, we could find O in terms of H
also distance to PSR = EO'H/(O'+H), using O' for distance out because groundspeed out to PSR/PET may not be the same as groundspeed on from PET (engine fail case etc. - similar arguments can be presented for H not being the same as H')
substituting...
(84/100)*1200 = (8.4*O'*H)/(O'+H)
Now at this point, if O and O' were the same, we could substitute our values for O in terms of H from the first formula and find a numerical value for H. We don't know this is the case, though, and so here I stop. My comments would be (i) that this is not a fair test of knowledge of formula, rather it is a test of maths and (ii) the solution relies on an assumption that we cannot make. All comments and corrections welcome.
Could you tell us which exam this appeared in, please, and which examining State?