Simplify using appropriate identity 0.85 × 0.85 +2 × 0.85 ×0.15 × 0.15

Remember that multiplication is to be done before addition or subtraction.  We see that both terms have the factor 0.85:

0.85 × 0.85 +2 × 0.85 ×0.15 × 0.15 =

0.85 * ( 0.85 + 2*0.15*0.15).  

This is equivalent to 0.85 ( 0.85 + 2*0.0225 ) = 0.85 ( 0.895 ).

This last result could be left as is, or evaluated with a calculator:

0.76075

56.6

step-by-step explanation:

the ratio of the perimeters is equal to the scale.

the ratio of the areas is equal to the square of the scale.

34 / 20 = k

a / 19.6 = k²

substituting:

a / 19.6 = (34 / 20)²

a = 19.6 (34 / 20)²

a ≈ 56.6