I have a good diet but my diet contains 12 biscuits(sorry but i eat them daily) which has 24gm carbs per 3 biscuits.Is there any way through exercise and how long the exercise should be and how many days per week to negate its bad effects on my body like fat due to lots of carbs.
As a rough guide, carbohydrates contain 4 calories per gram, so 24 / 3 * 12 * 4 will net you 384 calories. Assuming you're somewhere around 160 pounds (calories burning being dependent on a number of factors including age, sex, and weight), this chart shows that you'd need about an hour of mild aerobics, moderate elliptical training, or resistance weight training each day to "counteract" those calories. Of course, since your biscuits probably have calories from other sources, you're likely better off using the total calorie count on them. And, honestly, you're better off just reducing the total number of calories than trying to add exercise, because our bodies are built to consume more food in the face of exercise.
If you're just worried about the number of "carbs", I'd say that you're better off using other metrics for your diet. While there exist various low-carb diets, most of which are panned by medical personnel, they generally depend on actually eschewing the carbs entirely, not trying to "counter" them with exercise. Reduce your total amount of calories rather than trying to follow some fad of eliminating one food group or another.