Answer: 21
Step-by-step explanation:
Let the number be [tex]x[/tex] , then ;
[tex]\frac{5}{7}[/tex] of [tex]x[/tex] = [tex]15[/tex]
that is :
[tex]\frac{5x}{7}=15[/tex]
[tex]5x = 15(7)[/tex]
[tex]5x = 105[/tex]
divide through by 5
[tex]x = 21[/tex]
Therefore : the number is 21
