The Vandelay furniture company makes bookshelves and tables.

Consider the following Linear Programming Model:

X₁ = the number of bookshelves made in a day.

X₂ = the number of tables made in a day.

Maximize: Z = 50X₁ +50X₂ Profit ($)

Subject to:

20X₁ + 11.9X₂ <= 100 Labor (hours)

6.5X₁ + 10X₂ <= 50 Lumber (board-feet)

What's the lowest profit on a bookshelf can be, without changing the optimal solution?

Another way to ask this is, what's the lower bound on the sensitivity range for C₁?

(Round your answer to 1 decimal place.)