QR is 12, as you establish a proportion: 21/14 = x/8, then cross-multiply to obtain 14x = 168, which you solve by dividing to find x = 12.
x = 27 + 3 √ 129/ 4, 27 − 3 √ 129/ 4
Please note: the entire equation mentioned is divided by 4, not only the last term.
x approximates to 15.26836251, − 1.76836251
That concludes my response. I hope this is helpful. You will still need to work on finding y and z, which can be quite challenging:)
