Could u please provide me an answer to the following question?

Edmund has the following demand function for claret: q = 5+ 2m/10p, where m is income and p is price. Edmund's income is $50 and he initially had to pay a price of $2 per bottle of claret. The price of claret rose to $4. The substitution effect of the price change reduced his demand by [write just the number] Answer: 4 The correct answer is: