Calculus

The temperature T of a point with coordinates (x,y) lying in a region of the (x,y)-plane is given by the function

T(x,y)=3x^3-2xy+x-2y^2+3y

Show that the temperature is 1 at the point (1,-1).
At this point, determine the equation of the tangent to the T=1 contour of temperature, in the form y=mx+c, where m and c are constants that should be determined