please provide detail thx

Use the total differential to find the approximate change in z when (x, y) changes as indicated. (a) (3 points) z = f(x, y) = x2 + 3xy - 2y when (x, y) changes from (3, 1) to (2.98, 1.05). (b) (2 points) z = f(x, y) = 2x2 + y when (x, y) changes from (1, -1) to (1.02, -0.99)