Question 926557
Let x = the number added to numerator and denominator

If a certain number is added to both the numerator
and denominator of the fraction 7/9, the result is 5/7.

(x+7)/(x+9) = 5/7
 7(x+7) = 5(x+9)
 7x+49  = 5x+45
   2x   = -4
    x   = -2

The number is -2.

Check
(-2+7)/(-2+9)= 5/7
         5/7 = 5/7