Chord Ltd manufactures different types of guitars. Its best seller is the Atlantica. Chord Ltd plans to produce $600$ Altlanticas in the upcoming period. Material costs are $120$ per guitar. Each guitar uses $4$ Kg of material. The labour rate is $18\mathrm{.}50$ per hour and each guitar takes $3\mathrm{.}5$ hours to manufacture. Variable overheads are $20$ per unit. Fixed overheads attributed to the manufacturing of all Atlanticas are expected to be $60,000$ and absorbed on a per unit basis. Each Atlantica will sell for $350.$

What is the expected margin of safety in units?

$2,400$ units

$414$ units

$172$ units

$186$ units