Answer:
2018, and 2004.
Explanation:
do the math "using Your heads".
2018, 2004
substitute C(t) for 1274 because it's the cost
1274=6(t-11)^2+980
6(t-11)^2=294
(t-11)^2=49
x-11=7 x-11=-7
x=18, x=4
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