42x13-22x5+42x7-15x22
= 42 x (13+7) - 22 x (5+15)
= 42 x 20 - 22 x 20
= 20 x (42 - 22)
= 20 x 20 = 400
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37x39+78x74+13x85+52x55
= 37 x 3 x 13 + 13 x 6 x 74 + 13 x 85 + 13 x 4 x 55
= 13 x (37 x 3+ 74 x 6+ 85 + 4 x 55)
= 13 x (111 + 444 + 85 + 220)
= 13 x 860 = 11180
(637x527-189):(526x637+448)
= (637 x 526 + 637 - 189): (526 x 637 + 448)
= (637 x 526 + 448) : (526 x 637 + 448) = 1
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