Answer :

citroen
1) 10-2v=-5v-50 (add 5v on both sides)
    10+3v=  -50 (subtract 10 on both sides)
     3v  = -60   (divide by 3)
      v= -20
2) r+15= 4r-6 (add 6 on both sides)
    r+ 21= 4r (subtract 1r on both sides)
    21= 3r (divide by 3)
    7= r

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