Help me with this please

Context Free Grammars

1) Consider the following Grammar over alphabet: ={a,+,x,(,)}

E -> E+T|T

T -> T+F|F

F ->(E)|a

a) Give derivations for the following strings: a, a+a, (a)

b) Give parse trees for the following string:

a + a x a

2) Consider the grammar S -> aS | aSbS |

Show that the grammar is ambiguous by finding 2 different parse trees for the string aab

3) Give a grammar for the following languages:

a) L1 = {w|wcontains at least three 1s}

b) L2 = {w | length of w is odd}

c) L3 = {w | length of w is odd and the middle symbol is 1}