Vikram has written 4 of the 6 papers in an exam and his average so far is 63 marks. He wants his average over all 6 papers to be at least 70 marks. What is the least average he must score in the two papers still to come?

For an average of 70 over 6 papers he needs $6\times 70=420$ marks, and he already has $4\times 63=252$, so the last two papers must bring 168 marks between them - an average of 168/2 = 84. 77 repairs the 7-mark shortfall only once (70 + 7), but four papers fall short by 7 each, a deficit of 28 that only two papers can make good, so each must carry 14 extra. 168 is the total still needed, not the average. 70 is the target itself, which would leave the earlier shortfall unpaid.