In any triangle, the segment joining the mid-points of two sides is parallel to the third side and equal to half its length
B is the mid-point of RS
C is the mid-point of RT
BC = 1/2 ST
BC = x + 19
ST = x + 29
x + 19 = 0.5(x + 29)
x + 19 = 0.5(x) + 0.5(29)
x + 19 = 0.5x + 14.5
Subtract 0.5x from both sides
x - 0.5x + 19 = 0.5x - 0.5x + 14.5
0.5x + 19 = 14.5
Subtract 19 from both sides
0.5x + 19 - 19 = 14.5 - 19
0.5x = -4.5
Divide both sides by 0.5
The answer is D
x = -9