Answer:
 334 units sales increase during the month must be required to justify the contemplated expenditure
Step-by-step explanation:
If management proposes an increase in monthly promotional costs (which is a fixed cost), then the units required to at least cover these extra fixed costs (break -even) must be determined.
Break -even (units) = Fixed Cost / Contribution per unit
 = $1,600 / ($8.00 - $3.20)
 = $1,600 / $4.80
 = 333.333
 = 334
Therefore, 334 units must contemplate this expenditure