Answer:
The Dimension of new garden is 
Step-by-step explanation:
Given:
Perimeter of new garden = 70 feet.
Let the length of the new garden be 'l'.
Also Let the width of the new garden be 'w'.
We need to find the dimension of new garden.
Now Given:
Length is 5 feet shorter than three times it width.
framing the equation we get;

Now we know that;
Perimeter of rectangle is equal to twice the sum of length and width.
framing in equation form we get;

Now Diving both side by 2 using Division property of equality we get;

Now Substituting equation 1 in above equation we get;

Adding both side by 5 Using Addition Property of equality we get'

Now Diving both side by 4 using Division property of equality we get;

Now Substituting the value of 'w' in equation 1 we get;

Hence The Dimension of new garden is 