Hi! so you would find x by adding the corners up to 180 degrees.
steps:
Add the corners
90+(2x+1)+(5x+5)
7x+96=180
then subtract 96 from 180
you’d get 7x = 84
then divide 7 on both sides and get x=12
89kg in stones would be 12.598 stones
Well 1 percent is 0.9, so an easy way to work it out:
100(0.9)=90
10(0.9)=9
90+9=99.