Firm a Can Borrow at 4% Fixed or at Libor

Multiple Choice

Firm A can borrow at 4% fixed or at Libor flat in the fixed and floating rate markets, respectively. Firm B can borrow at 7% fixed or Libor plus 100 bps in the fixed and floating rate markets, respectively. A wants to borrow floating and B wants to borrow fixed. If A borrows fixed and B borrows floating and they enter into a fixed-for-Libor interest-rate swap in which A pays Libor flat, what is the range of fixed rates for B that enables each firm to improve its financing costs (compared to accessing financing in the market directly) ?

A) 4%-7%
B) 4%-6%
C) 5%-6%
D) 5%-7%