中1 英文數 help .....................

1.(a+b+1)(a+b-1) [Hint: consider x=a+b ]

2.(a+b+c+d)(a+b-c-d) [Hint:consider x =a +b and y = c+d ]

3.5times a number is greater than 3 times the number by 4.Find the number.
Solution : Let x be the number.


The number is ____________.

4. Aboy has twenty $2 coins and twenty $5 coins . In how many ways can be he but a gift that costs $96 if he pays the exact price for the gift?