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9 is an odd square number less than 10 and 92 = 81 which is greater than 50
x < 35 + 35 + 15x < 85x > 40 x 2x > 80Therefore x is between 81 to 84 (inclusive).The only number in this range in which the digits sum to 9 is 81.
81, 84 and 87. And 90 if you want to count that
25 is 56 less than 81.
In between .8 and .81 we find .805 (and infinitely many other numbers).