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C

Step-by-step explanation:

A, B and D are all only a few digits long and can be expressed as the ratio of two integers, where at least one is even:

A = -6/16 = -3/8, so it's rational

B = 7.0398 = 35199/5000, so it's rational

D = 6,907 = 13814/2, therefore rational

C, on the other hand is irrational.

If we simplify the surd √8, we get 2√2. The 2's on the top and bottom can now cancel out, giving us √2, which is irrational. [There's a proof but it's kinda long].

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