Twenty less than 8 times a number is the same as 15 more than the number written in number form

8x - 20 = x + 15

let x be the number.

twenty less than 8 times a number is 8x - 20

15 more than the number is x + 15

8x - 20 = x + 15
8x - x = 15 + 20
7x = 35
7x / 7 = 35 / 7
x = 5

To check:

8x - 20 = x + 15
8(5) - 20 = 5 + 15
40 - 20 = 20
20 = 20

Num of plants = (original#ofplants)*(1.6)^t