Help with Question

Dear coolcoolcool2016,

I'm happy to respond. Interesting: this is not a GMAT question, because it is a multiple choice with only four answers. What is the source of this question?

I would start with ratios & portioning.

The aspect ratio of the space is 3:2, 3 "parts" by 2 "parts," so the perimeter is 10 parts.
10 parts = 85 m
1 part = 8.5 m

This means that
length = 3 parts = 25.5 m
width = 2 part = 17 m

We can fit four of the (4m) x (4 m) spaces across the width, and up to six across the length. We could compute the area of the whole space (25.5. x 17, not a fun product) and subtract the total are of the workspaces (20 x 16). Instead, I think it's easy to consider the leftover spaces. See this diagram:
Probably the 20 workspaces wouldn't be crammed together like this, but arranging them like this makes it easiest to compute the leftover area, the area in blue.
Imagine a line from the lower right corner of the workspaces that goes horizontally to the right wall. This divides the blue into two rectangles.
The first is 25.5 m long and 1 meter high, with an area of A = 25.5 sq m
The second is 16 m tall and 5.5 meters wide.
We can use the doubling and halving trick for this second multiplication:
16 x 5.5 = 8 x 11 = 88
Add the two areas: 25.5 + 88 = 113.5 sq m

Answer = (C)

That's a great problem! Let me know if you have any questions.

Mike