The diagram tells you the total length of all sides of the garden is
... 0.5x + 45 + x + 2x = 3.5x + 45
The problem statement tells you this length is 150 ft, so we have
... 3.5x + 45 = 150
... 3.5x = 105 . . . . . . . subtract 45
... x = 105/3.5 = 30 . . . divide by the coefficient of x
Then 0.5x = 15 and 2x = 60.
Clockwise from left, the lengths of the sides of the garden are
... 15 ft, 45 ft, 30 ft, 60 ft