Explanation:
A.
the height, the 17cm leg and half of the baseline (16/2 = 8cm) create a right-angled triangle.
so, Pythagoras applies.
c² = a² + b²
c being the Hypotenuse (side opposite of the 90° angle).
so, we get
17² = height² + 8²
289 = height² + 64
225 = height²
height = sqrt(225) = 15cm
B.
the answer to this is the surface area of the whole box.
it has 5 sides :
bottom : 20×16 rectangle = 320 cm²
left and right : 20×17 rectangles = 340×2 = 680 cm²
front and back : 16×15/2 triangles = 120×2 = 240 cm²
in total that is
320 + 680 + 240 = 1,240 cm² of cardboard