Respuesta :

8a−4b=20 (1st)
5a−8b=62 (2nd)

multiply 
8a−4b=20 (1st) by 2
16a −8b = 40 (1st)
  5a −8b = 62 (2nd)
-------------------------subtract
11a = - 22
    a = -2

8a−4b=20
8(-2) −4b=20
4b = -16 - 20
4b = -36
  b = -9

answer
a = -2
b = -9