If you re-arrange 3x + y = 15 into y = -3x + 15 then sub it into the first equation you can solve for y : )
(-3x+15)^2 + y^2 = 85
(-3x +15)(-3x + 15) + x^2 = 85
(9x)^2 - 90x + 225 + x^2 = 85
(10x)^2 - 90x +225 - 85 = 0
either factor or use the quadratic formula to solve for x, then sub it back into 3x +y =15 and solve for y : )
Solve the system.
{x^2 + y^2 = 85
{3x + y = 15
1 answer