Does anybody know or can please verify if my solutions and answers are correct?
Your 1st 2 examples are correct - but your method is correct but more complex than needed. 

Voltages across resistors with the same current in them are proportional to the resistances. So if 1.25V drops across 125 Ohms, resistance for eg (10-1.25)V is 8.75*  125 Ohms = ....

Your last example appears to be numerically wrong even though the method looks OK.
I suggest you try using the above method which is based on the same theory but simpler to apply.
eg for 25Vout and V_125_Ohms =  1.25V.
1.25V is dropped across 125 Ohms,
so 23.75 V  is dropped across = 23.75/1.25 x 125 Ohms = 2375 Ohms.
(The 125 Ohms is contrived to allow solution "by inspection")