Respuesta :

Answer:

315 cm²

Step-by-step explanation:

Given the scale factor of 2 similar figures is a : b , then

ratio of areas = a² : b²

Here the scale factor = 7 : 21 = 1 : 3 , thus

ratio of areas = 1² : 3² = 1 : 9

That is the area of the enlargement is 9 times the original, so

area of enlargement = 35 × 9 = 315 cm²

Answer:

increase by a factor of 3

Step-by-step explanation:

First you have to find the width,

35/7=5cm

Since the length had been increased to 21cm, we need to find the larger area,

21*5=105cm^2

now we just need to find how much has the area increased compare to the original area,

105/35=3

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