Let's assume
width =w
length=l
we are given
The width of a rectangular garden is 6 meter less than the length of the length of the garden
so, we have

we know that
Area = length*width

we are given
the area of the garden is 78 square meters
so, we can set A=78

now, we can plug for w


now, we can solve for l
we get

now, we can find w


so, dimensions are
length is 12.3m
width is 6.3m................Answer