5x5. 25 lbs in 3 months is a lot but it can be done and with a small amount of it fat. Eat until you can't eat any more, wait 2 hours, repeat, wait 2 hours repeat, etc. etc.
If you really want the 25 lbs take in 5500-6000 calories a day, most of that coming from quality foods. Im talking a truckload of chicken, beef, brown rice, oats, weight gainer, milk, cheese, whole wheat bread, eggs, cottage cheese, fish, and on and on. Don't be afraid of a little bit of junk food, just don't over do it. try to take in 2-2.5 grams of protein per pound, 4-4.5 grams of carbs per pound of bodyweight, and about .75 grams of fat per lb. This is just a rough estimate, and many will disagree that this is too much food, but I say, eat even more than this, shoot for 6500 calories and 3 grams of protein per pound.
It is extreme to do all this but if you want the 25 lbs bad enough then it is all within reach.
P.S.- I hope you have a good amount of $ for these next 3 months because its going to cost you an arm and a leg.