If x + y = 8 and y − 3x = 7, then what is the value of y-x? Choose the correct choice:
A) 1/7 B) 3 C) 15 D) 15/2 E) 60/7
x+y=8 ...equation 1   -3x+y=7 ...equation 2   adding both the equations   -2x+2y=15=&gt;y-x=15/2   correct answer option 15/2
<result>D</result>
If x + y = 8 and y − 3x = 7, then what is the value of y-x?