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Explanation:
The sides are in the ratio 4:7:10
This scales up to 4x:7x:10x showing that the sides are 4x, 7x and 10x. The variable x is some positive real number.
Add up the sides and set this equal to the given perimeter 105. Solve for x.
4x+7x+10x = 105
21x = 105
x = 105/21
x = 5
This value is then plugged into each side
The triangle has sides of 20 cm, 35 cm, and 50 cm.
Note how the ratio 20:35:50 reduces to 4:7:10 after dividing all three parts by the GCF 5. Also, we can see that 20+35+50 = 105 to fully confirm our answer.