Hi Maria,

Since the number is even its units digit must be even, that is 0, 2, 4, 6, or 8. Suppose the units digit is 8 then the sum of the other two digits is $15 - 8 = 7.$ Find two digits which have a sum of $7.$ That gives you a number that could be Sue's favourite. Find another two digits which have a sum of $7.$ Remember that if the sum of two digits is $7$ you can switch their order and the sum is still $7.$ Watch out that your son doesn't make the hundreds digit of Sues favourite digit a $0,$ because then it is really a two digit number.

Once you have found some possibilities consider numbers where the units digit is $6.$ In this case what is the sum of the other two digits?

I hope this helps,
Penny