Hey there!
Find molar mass of C₆H₂Cl₄.
C: 6 x 12.01
H: 2 x 1.008
Cl: 4 x 35.45
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215.876g
This is the mass of 1 mole of C₆H₂Cl₄.
Multiply 215.876 by 5.99.
215.876 x 5.99 = 1293
The mass of 5.99 moles of C₆H₂Cl₄ is 1293 grams.
Hope this helps!