First one simplifies to 2x + 6 = 2x + 7 which can't be true so this one has No Solution.
Same applies to the second equation ( 5x + 15 = 5x - 15) No solution
also the last one has no solution because it simplifies to 4x + 20 = 4x + 19
Answer:
So x = 20
Step-by-step explanation:
AB + BC = AC sum of a segment is sum of its pieces
AB + AB = AC B is the midpoint, so AB = BC
2x + 2x = 3x + 20 putting in for AB (twice!) and AC
4x = 3x + 20 collect like terms
x = 20 subtract 3x on both sides.
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There are many possibilities. An example is 
.
5x + 2y =9
X + y= -3
5x+2y=9
2x+2y=-6
__________
3x =15
X =5
5+y=-3
Y=-8
Answer is : (5,-8)
