Your question is quite incomplete: who's k?
Anyway, I'm assuming that this is one of those question about variation. If x and y are in proportion, we have

If x and y are in inverse proportion, we have

Answer:
-5, -3, 0, 4, 6
Step-by-step explanation:
2/3 is just .6666666666 and the 6 goes on forever
Unit rate means how much does it cost for 1 unit
140 for 18ft^2
divide by 18
140/18=7.77777777777777
so the unit rate is $7.78 per square foot
Check the picture below.
now, we know that the slanted legs are congruent, since it's an isosceles trapezoid, we also know that the bases are the parallel sides, so, the "altitude" or distance from those bases are the same length, for each of those triangles in the picture.
now, the bases are parallel, that means the altitude segment is perpendicular to the base, the longest side at the bottom, so, we end up with a right-triangle that has a Hypotenuse and a Leg, equal to the other triangle's.
thus, by the HL theorem for right triangles, both of those triangles are congruent, and if the triangles are congruent, all their sides are also, including the ones on the base.