Please note the two parts in this question are not related. (a) Find an equation of the tangent plane to the surface of z = 3ygl2$s+yzlat (1: _2: _6) (b) Given that the function z = 313,49) is a differentiable function with f(1,3) = 4, f1:(13 3} = 1, fy[1,3} = 2, find the linear approximation and the differential of the function at (1.3). Use the differential to estimate the total change AZ when x is increased by 0.03. and y is decreased by 0.02. Enter your answer in the blank below. Round your answer to two decimal places