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The LCM is 2, Because 2*4=8 and 2*50=100 :)
Find the ratio of the known sides.
6/4 = 1.5
The larger triangle is 1.5 times larger than the smaller one.
Area is in square units, so to find the area of the larger triangle square the ratio and multiply that by the area of the known triangle.
1.5^2 x 40 = 90 square cm.