Answer:
56cm
Explanation:
Ratio = 3 : 5 : 7
Perimeter = 120 cm
Process
# of parts = 3 + 5 +7 = 15
Divide 120 by 15 = 120 / 15
Number of parts = 8
First side = 3 x 8 = 24 cm
Second side = 5 x 8 = 40 cm
Third side = 7 x 8 = 56 cm
Perimeter = 24 + 40 + 56 = 120 cm