Ok, so
We got the situation here below:
We know that the area of the garden is 690 m².
So, we got that the height (1+3x) multiplied by the width (x), should be equal to 690.
[tex]\begin{gathered} (1+3x)(x)=690 \\ x+3x^2=690 \end{gathered}[/tex]
We have to solve:
[tex]3x^2+x-690=0[/tex]
If we solve this quadratic equation, we obtain two solutions.
One of both solutions is negative, so we will not use it.
The second one is positive and equals to 15. So, x=15.
Now that we know that x=15, we replace:
x, (Width) is equal to 15 meters.
1+3x (Length), is equal to 46 meters.
Therefore, these are the dimensions of the garden.
Width: 15 meters
Lenght: 46 meters.
