Set the first integer to X. The subsequent integers would be increasing in steps of "1," since they are all integers, also.
Do as the sentence says by adding the first three and then subtract 3, since that number is now equal to the sum of the last 2 integers. Then simplify the equation and you'll find that X = 7. Just keeping adding 1 to get the next digits, as I've summarized below.
x = 7
I hope this helps,