A block of balsa wood placed in one scale pan of an equal-arm balance is exactly balanced

Question:

A block of balsa wood placed in one scale pan of an equal-arm balance is exactly balanced by a 0.0950-kg brass mass in the other scale pan. Find the true mass of the balsa wood if its density is 150 kg/m'. Explain why it is accurate to ignore the buoyancy in air of the brass but not the buoyancy in air of the balsa wood.