Answer: 27 rows contain 25 vines.
Step-by-step explanation:
Let x represent the number of rows that contain 20 vines.
Let y represent the number of rows that contain 25 vines.
Sarah plants 760 vines in rows containing either 20 vines or 25 vines. This means that
20x + 25y = 760- - - - - - - - - - -1
There are 3 times as many rows containing 25 vines as there are rows containing 20 vines. This means that
y = 3x
Substituting y = 3x into equation 1, it becomes
20x + 25 × 3x = 760
20x + 75x = 760
95x = 760
x = 760/95
x = 9
y = 3x = 3 × 9
y = 27
