This question has an error, the cake cost $17 each instead of $7.

B [u][u][u][u]  —-$3

C [u] —$17

17u – 3(4u) = 55

17u-12u = 55

5u = 55 => u=11

Hence buns bought = 11 x 4 = 44

How did you know about the error?  I would have just been left scratching my head lol.

7u -12u is a negative number and even if absolute value is taken, it shows that he would spend more on the buns than the cake which is not what the question has stated.

Yes.  But how did you figure out that it was $17 instead of $7?

Sorry I did not see your question until today.

It’s an educated guess since this is a whole number question.  17-12 = 5 and 55 is divisible by 5 plus most likely the printing error is short of a ‘1’ as the probability of it being a number completely off from ‘7’ is low.

Oh I see… it’s a guess but a very good educated guess 🙂  I thought you had access to the teacher who set the question or something 🙂