Ответ:

{ 3(x+2y)+5(3x-y)= 75

{ 2x-3y= -1

{3x+6y+15x-5y= 75

{ 2x-3y= -1

{ 18x+y = 75

{ 2x-3y = -1

y = 75-18x

2x-3(75-18x)= -1

2x-225+54x= -1

56x= 224

x= 4

y= 75-18×4 = 3