Given:
Height = 4 feet
Base = 6 feet
so,
Area of triangle = 1/2 x b x h
= 1/2 x 6 x 4
= 12 feet squared
Area of rectangle = length x width
= a x 6
= 6 a
Total area = 6a + 12
The maximum area = 150 ft^2
Using inequality
6a +12 must be less than or equal to 150
6a less than or equal to 150-12
6a less than or equal to 138
a less than or equal to 138/6
a less than or equal to 23
Hence,
The length of the rectangle should be less than or equal to 23 feet.