Ok. just did this last lesson and need to revise so i'll try and help.
Firstly equilibrium = point where 'supply=demand'
If consumers will demand 10000 units of a product priced at $10 and Suppliers produce 10000 units this would be the equilibrium point (no unsold goods and no customers unable to get hold of the goods)
If the suppliers put the price upto $15, Consumers would only demand 8000 units. So the supplier would have to cut the ammount produced or there will be excess supply.
These are goods which consumers tend to purchase together eg, hamburger buns and burgers(beef).
If the wheat production falls the price of buns will rise as suppliers are supplying a smaller number.
Thus less consumers purchase the buns. Equilibrium price rises. Quantity falls
This effects beef sales because people wont want burgers without buns.
Results in less demand so companies cut back supply and raise price. Equilibrium price rises. Quantity falls.
Substitute goods also come into this eg. If beef prices rise due to less demand more people will choose to buy pork as a substitute. Pork prices will drop and quantity demanded and supplied will rise.
Thats what i came up with quickly, might not have helped. let me no if you need more. i expect someone should be able to explain this better.