(a) Here is part of a number grid. A square can be placed anywhere on the grid outlining four numbers. The numbers in opposite corners of the square are multiplied together and the difference between the products is found. [Table] 9×14-8×15 = 126-120 = 6 (b) Here is part of a different number grid. A cross can be placed anywhere on the grid outlining five numbers. The numbers in the cross are added together. [Table]

1. (a)(i)The grid is continued downwards. If n represents the number of the top left of the square, complete this square with expressions for the other numbers. n n+1 (blank) (blank)[1]
2. (a)(ii)Use your answer to part (a)(i) to prove that the difference between the products of the opposite corners is always 6.[2]
3. (b)(i)Find and simplify an expression, in terms of n, for the sum of the numbers in the cross below. n (empty cross)[2]
4. (b)(ii)The sum of the numbers in the cross below is 330. Complete the cross with the correct numbers. (empty cross)[2]