I’m not sure if this is correct but
you have used 3/8 of the plants so you will have 5/8 left to use
If I understand the question, you have to get n alone. in this case, you have to subtract 7 from both sides, resulting in n (is less than) -10
20 - 21 - 10 + 5x +1= 0
5x = 10
x = 2
Y=-5.11111 how I solved it is in the picture attached