Do any constraints have (nonzero) slack? If yes, which ones and how much slack does each have ...

Use simultaneous equations to determine the optimal values of the decisions variables. I am also asked to show GRAPHS and explain my work.
 

Maximize Z=6A+3B(revenue)

Subject to

Material 20A+6B<=600lb

Machinery25A+20B<=1,000hr

Labor 20A+30B<=1,200hr

A,B>=0

1. What are the optimal values of the decision variables and Z?

2. Do any constraints have (nonzero) slack? If yes, which ones and how much slack does each have?

3. Do any constraints have (nonzero) surplus? If yes which ones and how much surplus does each have?

4. Are any constraints redundant? If yes, which ones? Explain briefly.