If the radius of a cylinder is doubled

If the radius of a cylinder is doubled and so is the height, how much bigger is the new lateral surface area (with out the bases)?
(a) 8.
(b) 2.
(c) 6.
(d) 4.
(e) 10.

The best answer is D.
The lateral surface area of a cylinder is (2 x pie x R) x (height of cylinder).
The new lateral surface area is (2 x pie x 2R) x (double the height) = 4 times bigger.

 If  X ~ Y = X^2 + XY, then what is the value of  -1 ~ 2 ?
(a) 1.
(b) -1.
(c) 3.
(d) 4.
(e) 2.

The best answer is B.
-1 ~ 2 = (-1)2 + (-1)2 = -1.