.
I interpret the problem this way.
The bed is 27 ft long.
Maria will plant flowers in the center of each of 27 one-foot interval.
So, she will plant 27 flowers.
Starting from this point, everybody can continue and complete the solution to the end.
Solved.
/////////////////////////////////
After the post from @greenestamps, I see the necessity to explain in more details,
why I chose that interpretation, which I used in my solution above.
The instruction " to space the plants 1 foot apart " translated to terms of biology of the plants
and to common sense, means that every plant requires the space of 1/2 ft from each side for normal growth.
It leads directly to that interpretation, which I used in my solution.
So, my interpretation is consistent with the instruction and with the common sense.