I don't understand how to set up an equation for question 15 (eg. let x be the total amount of fish)

how to draw the joint ppc with the slopes derived form opportunity cost to do Q13

I have no idea for 18 also...

Question 15 Not complete Marked out of 1.00 \\V Flag question In a closed economy, Ann and Bruce shall make their production and consumption decisions together. Ann can produce either 7 kg Fish or 4.2 kg Mushroom per day. Bruce can produce either 6 kg Fish or 15 kg Mushroom per day. Suppose now they decide to consume Fish and Mushroom at a ratio of 2:1. Ann and Bruce will consume [Answer] kg Fish per day. (In decimal numbers, with two decimal places, please.) Question 18 Not complete Marked out of 1 .00 \\V Flag question In Islandia, a small economy, Jack and Jill shall make their production and consumption decisions together. Jack can produce either 8 kg banana or 12 kg tea per day. Jill can produce either 10 kg banana or 23 kg tea per day. Suppose now they are open to trade with the rest of the world. The price of banana is $3.5/kg and the price of tea is still $1/kg in the world market. Suppose Islandia is small enough that its behavior will not affect the world prices. Jack and Jill will produce a total of [Answer] kg banana per day. (In decimal numbers, with two decimal places, please.) Question 13 Not complete Marked out of 1.00 \\V Flag question In a closed economy, Ann can produce either 7 kg Fish or 4.2 kg Mushroom per day. Bruce can produce either 6 kg Fish or 15 kg Mushroom per day. Which of the following points is NOT on their joint production possibility curve? (In the form of [Answer01] kg of Fish and [Answer02] kg of Mushroom.) Select one: Q a. 7,15.00 0 b.13.00,0 O c.3.5o,17.1o 0 d. 9.00, 7.50