In a right triangle, one angle measures x°, where sin xº 4/5
What is cos(90° - xº)?

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Rule:

if A+B = 90, then cos(A) = sin(B) and sin(A) = cos(B)

This can be rephrased into cos(A) = sin(90-A) and sin(A) = cos(90-A)

We'll focus on the second case sin(A) = cos(90-A)

Simply replace A with x and we have the same idea.

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So,

sin(x) = cos(90-x)

cos(90-x) = sin(x)

cos(90-x) = 4/5

You can prove this by drawing out a right triangle as shown below.

18

step-by-step explanation:

draw the shape and you will see that f and k are actually at adjacent vertices (points of the hexagon that are neighboring).   so find the distance between (1,2) and (4,2).   that is easy since (1,2) and (4,2) is just a vertical distance to count, which is 3.   it is a regular polygon which means all sides are congruent.   you have 6 sides (hexa) so multiply 6 by 3 to receive 18.