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206.

-1/4 * 8/6 - 7/18 * 9/21 = -1/3 - 1/6 = -2/6 - 1/6 = -3/6 = - 1/2,

221.

15 * (1 + 1/3 - 1/5) = 15 * (15/15 + 5/15 - 3/15) = 15 * 17/15 = 17,

235.

3/10 * (-5/6) + 2/3 * (-3/8) = - 1/4 - 1/4 = - 2/4 = - 1/2,

234.

(8/11 - 20/55) * 66/20 = (40/55 - 20/55) * 66/20 = 20/55 * 66/20 =
= 66/55 = 6/5 = 1 1/5