These inequalities follow straight from your problem statement - they have to hold!
The only question is, what restrictions do they place on s and t exactly?
Yes, t has to be greater than or equal to zero and less than or equal to 2+s.
But the 2nd and 3rd inequality place further restrictions on t... but which restrictions?
Which inequalities do you get in those cases?
Alternatively can you make a graph with:
- s on the horizontal axis
- t on the vertical axis
- the line l given by t=(-4 + 7s)/9
- the line m given by t=(-4 + 7s)/19
We would be looking for values of t that are above line l and below line m.