A equals -1/2 is the right answer
The answer to your question is the last one.
Answer:
X= 30-4r/-6
Step-by-step explanation:
1. Move the 9 to the other side. (21+9=30)
2. subtract the 4r and move it to the other side (-6x=21-4r)
3. divide both sides by -6
let the width of the rectangle be x
area of rectangle is l*b
x * (x + 6) = 40^2
x^2 + 6x = 40^2
x^2 + 6x = 1600
x + 6x =√1600
x + 6x = 40
7x = 40
x = 5.7
Hope you found this useful