As others have said 40lb in 10 weeks will not be possible but you could potentially do 15lb which will make a big difference and have you heading in the right direction.
I don't love meal replacements, they haven't worked for me in the past and I've just been hungry and miserable but that doesn't mean they won't work for you.
Go to a TDEE calculator and put in your numbers to calculate how many calories you can eat to maintain your weight. then deduct 500 from your maintenance number and that should be a good indicator of how many calories you can eat and lose weight. It's only a guide so you may need to adjust up or down a little.
Add in some exercise, weight loss is mainly about what you eat but exercise strengthens your muscles, increases your fitness, improves your posture so that you look slimmer, it also boosts your confidence which makes a world of difference. I like this free exercise program, they have a YouTube channel too if you prefer it.
ourparks.org.uk/couch-to-fitness
https://www.youtube.com/playlist?list=PLzyGqy4hi5yAr4wQImo5HgwZIZ58PVyY-
It's taken me 8 months but I'm 57lb down with 12 left till I hit the healthy BMI.
My best diet tip is to cut down on carbs as they tend to be high calorie and replace with green veg like green beans, baby corn, mange tout, asparagus which you can have load of they're about 49 cals a cup full. When you do have carbs go for whole grains and seeds which will fill you up for longer so worth the higher calories. It's always frustrating when you have something like white bread, 2 slices comes in at about 250 calories, then you add spread, light Mayo, salad and meat for a sandwich and its 400-500 calories and you're hungry an hour and a half later.