.
Let x be her speed walking, in miles per hour (the unknown value under the problem's question).
Then her speed riding is (x+9) mph.
Now I write the "time" equation, as I read the problem
     =
 =  .
Next, to solve it, cross-multiply and simplify
    5(x+9) = 23x
    5x + 45 = 23x
    45 = 23x - 5x
    45 = 18x
     x =
.
Next, to solve it, cross-multiply and simplify
    5(x+9) = 23x
    5x + 45 = 23x
    45 = 23x - 5x
    45 = 18x
     x =  = 2.5 mph.
ANSWER.  Her speed walking is 2.5 miles per hour.
 = 2.5 mph.
ANSWER.  Her speed walking is 2.5 miles per hour.
Solved, with all necessary explanations.