In the arrangement shown in the figure pulleys are small, light and frictionless, threads are inextensible and mass of blocks `A`, `B` and `C` is `m_(1)=5kg`, `m_(2)=4kg` and `m_(3)=2.5kg` respectively and co-efficient of friction for both the planes is `mu=0.50`. Calculate the acceleration of block `A` (in `m//s^(2)`) when the system is released from rest. (`g=10 m//s^(2)`)