Answer:
C. The bar weighs 45 lb without any plates.
Step-by-step explanation:
The weight of "2 plates" is really "2 plates + 1 bar". Doubling that value, we get ...
2(2 plates + 1 bar) = 4 plates + 2 bars = 2(115 lb) = 230 lb
The second line of the table, for "4 plates" is really "4 plates + 1 bar". Subtracting that from the number just computed, we have ...
(4 plates + 2 bars) -(4 plates + 1 bar) = (230 lb) -(185 lb)
1 bar = 45 lb . . . . . . simplify
