Questions below followed by three quantities. Find the relation between them.

Quantity I: Out of a certain sum, 1/4th of sum is invested at 6% per annum, out of remaining half amount invested at 8% per annum and remaining amount is invested equally in two parts at 10% per annum and 14% per annum, If all parts were invested for three years on simple interest and total interest of Rs. 10800, find the original sum?

Quantity II: Mohan divided Rs. 10000 between his two sons aged 12 years and 14 years such that both of them would get an equal amount when elder son lent at the rate of 35% SI and younger son lent at the rate of 10% SI after they attain 18 years of age. What is the share of younger son in Rs. 10000?

Quantity III: A sum of Rs. 24000 is divided into two parts. One part is lent at the simple rate of interest 10% per annum and the other at 12% per annum. After 6 years the total interest received is Rs. 15480. The sum lent at the rate of 12% simple interest is?