Answer: 26 mm
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Work Shown:
(39 mm)/(6 m) = (x mm)/(4 m)
39/6 = x/4
39*4 = 6*x
156 = 6x
6x = 156
x = 156/6
x = 26
The actual length of 4 meters corresponds to 26 mm on the blueprint.
Side note: I used the cross multiplication rule on the third line.
