Basically for this question, to solve for p and q, you need to find the cases that fulfil the condition that the vectors U and V are non zero and non parallel. For them to be non- parallel, either (q-3) or (p+4) must be zero. if they are not zero, vectors U or V can be expressed as multiples of each other which implies that they are parallel, which they are not. thus both (q-3) and (p+4) must be zero so that the equation can be be valid.