a) x + 54 cm 9 mm = 7 dm 8 cm
54 cm 9 mm = 549 mm
7 dm 8 cm = 700 + 80 = 780 mm
x = 780 mm - 549 mm
x = 231 mm = 23 cm 1 mm
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b) 0,42 m - x = 29 cm 6 mm
x = 0,42 m - 29 cm 6 mm
x = 42 cm - 29 cm 6 mm
x = 420 mm - 296 mm
x = 124 mm = 12 cm 4 mm
