Ola Luis

3t + 5r = 7

2t - 4r = 9

2t = 9 + 4r

t = (9 + 4r)/2

3t = (27 + 12r)/2

(27 + 12r)/2 + 10r/2 = (22r + 27)/2 = 14/2

22r = 14 - 27 = -13

r = -13/22

3t - 65/22 = 154/22

3t = 219/22

t = 219/66 = 73/22

pronto