Inequality would be: 6 + 3x ≤ 40
Subtract 6 from both sides,
3x ≤ 34
Divide both sides by 3,
x ≤ 11.33
As number of rides can't be in decimal, greatest number of ride, she can go on would be nearest smaller value which is 11
In short, Your Answer is 11
Hope this helps!