(5,12,13) is a right triangle and can be constructed.
All the others do not satisfy the triangle inequality, i.e. the sum of two short sides must exceed the long side in order for the triangle to be constructed.
Examples:
2+11<15, so no
3+7<11, so no
4+8<15, so no
but 5+12>13 so yes, it can be constructed.
3.) 5x-6=0, Add 6 to either side -> 5x=6, divide each side by 5 -> x=6/5 ---- 4.) x+y/3=5, multiple each side by 3 -> x+y=15, move y to the other side -> x=-y+15
