Hi Mike,
You have now 95.15% gas (and 4.85% oil) [calculated: 25 * 100/26]. That means 30.77 oz gas. In 40/1 the percentage is 97.56%. The equation is
(30.77 + X) * 100 /(32 + X) = (32 + X) * 97.56/100
X= 18 oz
If I dibn't go wrong along the way you need to add 18 oz of gas.
Best regards,