Statistics, two products made of same two materials, max price I can't solve this problem:
You have two products, which consist of two materials. First one has a price of 3 units, second is worth of 2 units. For fist one you need 2 pieces of first material and 4 pieces of second. For second product you need 1 piece of first material and 5 pieces of second material. Also you can spend 180 pieces of first material and 600 pieces of second material.
How many first one and how many second one products should be made, that the price would be maximum?
How much the price of first product can be changed and the optimum is still the same? 
P.s. what is the optimum?
Thanks in advance for answers.

Excel is your friend. 
The answers are:
1) The maximum income is 310, which happens when 50 units of the first product and 80 units of the second product are made. 
2) The price of the first product can be reduced to 1.6 and the maximum income will still occur at 50 and 80. However, it will also occur at other combinations and will only be 240.
3)The optimum is 310.
I know you would like equations to support the results above, so I'll try and find them. 
