Department $3$ has $2500$ hours. Transfers are allowed to departments $2$ and $4,$ and from departments $1$ and $2.$ If Ai measures the labor hours allocated to department i and Tij the hours transferred from department i to department j$,$ then

a$.$

T$31+$ T$32$ T$23$ T$43+$ A$3=2500$

b$.$

A$3+$ T$13+$ T$23$ T$32$ T$34=2500$

c$.$

T$13+$ T$23$ T$32$ T$34$ A$3=2500$

d$.$

A$3$ T$13$ T$23+$ T$32+$ T$34=2500$