Limiting Factor Analysis – SLACK AND SURPLUS

Good day to all,

I am using BPP Text Book, December 2014 and June 2015 Exam Sessions

My question comes from Chapter 4, Section 6, SLACK AND SURPLUS

the book only gives one example which is about a factory which produces BOXES and TINS

3B+10T less than or equal to 330. (sorry but I can’t find the sign)
16B+4T less than or equal to 400
6B + 6T less than or equal to 240
T greater than or equal to 12
B greater than or equal to 0

the optimal solution is 10 Boxes and 30 Tins

the book does not show the working, could someone please explain the working for this problem for me please.