The first number is 8
Solution:
Let the first number be "x"
The second number is 6 times the first
Second number = 6x
The third number is 15 less than the second
Third number = second number - 15
Third number = 6x - 15
The sum of three numbers is 89
Therefore,
First number + second number + third number = 89
[tex]x + 6x + 6x - 15 = 89\\\\13x - 15 = 89\\\\13x = 89+15\\\\13x = 104\\\\Divide\ both\ sides\ by\ 13\\\\x = 8[/tex]
Thus the first number is 8