Given that the solution of the system of equations {ax by = 4, BX + ay = 5 is {x = 2, y = 1, then a + B = ()

Given that the solution of the system of equations {ax by = 4, BX + ay = 5 is {x = 2, y = 1, then a + B = ()

From the meaning of the title
2a-b=4(1)
2b+a=5(2)
(1) * 2: 4a-2b = 8 (3)
(3) (2) 5A = 13, a = 13 / 5
When a = 13 / 5 is brought into (1), 2 * 13 / 5-b = 4, - B = 4-26 / 5, - B = - 6 / 5, B = 6 / 5
So a + B = 13 / 5 + 6 / 5 = 19 / 5