Ihave just learned linear programming and need extra finding the constraints (there are four).

the wheelie manufacturing company makes bicycles and tricycles. in order to meet demands of its retailers, the company must make at least 20 bicycles and 30 tricycles each day. at most twice as many tricycles as bicycles can be made in a day. a total of only 90 bicycles and tricycles can be made each day. the profit on each bicycle is $17 and the profit on each tricycle is $21. how many bicycles and tricycles should be made in order to maximize the profits?