Since the angle given is 30 and the four lengths given are equal corresponding the angles opposite to their given sides for the top left triangle and bottom right triangle, the corresponding angles are equal and also 30 degrees. Since x is where the top left triangle is, we need an equation to relate x. The sum of all the angles in the top left triangle is 180. So, x + 30 + 30 = 180.
It would take 70,000 seeds if five out of seven are good. So over a quantity of 50,000 plants desired, you would sow 70,000 seeds. As 20,000 would statistically fail.