600 soldiers in afort had enough food for 14days .After 4days some soldiers were transferred to another fort and thus the food lasted for30more days . How many soldiers left the fort

Let each soldier eat 1 unit of food daily , so for 600 soldiers ,600 unit of food is required per day

And for 14 days, 600 * 14 =  8400 units of food is available.

And the soldiers left after eating 4 days , so they have eaten 600*4 = 2400 units.
So food left = 8400 - 2400 = 6000 units

And this 6000 units is enough for 30 days.
Let there are x soldiers left in the fort .
Hence x unit is required daily 
So for 30 days 30x is required .
And this 30x = 6000 units
Hence x = 200
So only 200 soldiers are left in the fort and 400 have left the fort.

Hope you have got it.