The square of a binomial expands as follows:

Expanding all the binomials, we have

Sum like terms:

Simplify terms appearing on both sides:

Move all terms involving k to the left and all numbers to the right:

Divide both sides by -20:

Answer:
17.9 units is the answer
Step-by-step explanation:
points are (-7,-2) and (9,6)
Pythagorean theorem can be written as,

Rounding off,
d = 17.9 units
30% of 42 is 12.6$.
42-12.6 = 29.4$ is the price of the pair with discount applied.
Tax 7%
29.4 * 7% = 2.06
29.4$ + 2.06$ = 31.46 $ final price with discount and tax applied.
X/7 = 6/4.2
4.2x = 42
x= 10