Brain-Teaser 486

From The Sunday Times, 20th September 1970 [link]

So as to encourage my four children to practise their arithmetic I have invented a game played with a standard pack of playing-cards. For scoring purposes an Ace counts as 1; Jack, Queen and King as 11, 12 and 13 respectively; and each other card by its numerical value.

To make matters a little complicated, I decided that Hearts should count at face value, Clubs at double value, Diamonds at triple value, and Spades at quadruple value. Before each deal, one card is extract from the pack, and a Joker, valued at 50 points, is substituted.

The cards are then dealt in the normal manner, and each child then counts up the points value of his or her hand. There is a small reward for the child who most rapidly correctly counts up his points, but the winner is the child with the highest total.

At the conclusion of one such game, each of the totals was an exact multiple of 7, and the winner, Bert, had scored 42 more than Amy, who had beaten Don by 35. Poor Clara came last with 14 points fewer than Don.

Which card had been replaced by the Joker?