The system of inequalities is
25x + 15y >= 100
x + y <= 6
where x are hours to build and y are hours to update.
The first inequality could be simplified, so the final system is
5x + 3y >= 20
x + y <= 6
Usually, the conditions of non-negativity x >= 0, Y >= 0 also are attached to the system.
One of possible solution is x= 4, y= 0.
Another possible solution is x= 4, y= 1.
You can easily guess other possible solution/solutions.