Then x+3y=550 (1)

3x+y=600 (2)

Then 3*( 1)-(2)

8y=550*3-600= 1050

Then y =1050/8 =131.25.

Then x = 550-3y = 550-3 *131.25 =156.25.

Then 1 ton a and 1 ton b are 156.25 yuan, 13 1.25 yuan respectively.

Something like this