Answer:
Is it not 2x + 12?
Step-by-step explanation:
The volume is the product of the side lengths which is 1*6*11= 66 mm^3. The surface area is twice the sum of all the possible products of the side lengths, or 2lw+2wh+2hl which is 2(6*11+6*1+11*1) = 166 mm^2 if my mental math is decent.
A rectangle with sides 15 and w has perimeter

We want this quantity to be at most 50, so it must be less than or equal to 50:

For the record, this implies that

So, the width can be at most 10.