Combining Like Terms

Which of these are like terms in the following expression:
3x + 7 - 9x + 24y + 2x²

• 7, 24y
• 3x, 9x
• 3x, -9x
• 3x, -9x, 2x²

Simplify by combining like terms:
5a + 2b - 3a + 4

• 8a + 2b + 4
• 2a + 2b + 4
• 8ab
• 4ab + 4

X+X+X+X+X

• X + 5 
• 5X
• X+X+X+X+X+5
• X to the 5th power 

a + a + a + a

• a + 4 
• 4a 
• a to the fourth power 
• 4a + 4 

2r + 2 + 5r - 2 + r 

• 8r 
• 8r - 4 
• 12r 
• 7r + 4 + r 

y + x + y + y + x 

• 2 + 3 
• x + y 
• 2x + 3y 
• 5xy 

6x + 1 + 7x 

• 13x - 1
• 14x 
• 7x + 6x + 1 
• 13x + 1 

2(4 + 9w) 

• 8+9w
• 2+9
• 8+18w
• 2+9w

7(y+9)

• 7+9
• 7y+63
• -7y-63
  -7y+63
• 7x+63

2(4X-7)

• 8x-14
• 8x-7
• 6x+7
• 8x+14