Answer:

1. Find the sum of (7x²-3x-8) and (-3x²-9x-7).

Solution:

• (7x²-3x-8)+(-3x²-9x-7)
• 7x²-3x-8-3x²-9x-7
• 7x²-3x²-3x-9x-8-7
• 5x²-12x-15

Answer: 5x²-12x-15

2. Find the difference between (y⁴+5y³+y²-y+20) and (y⁴-12y³+y-4).

Solution:

• (y⁴+5y³+y²-y+20)-(y⁴-12y³+y-4)
• y⁴+5y³+y²-y+20-y⁴+12y³-y+4
• y⁴-y⁴+5y³+12y³+y²-y-y+20+4
• 17y³+y²+24

Answer: 17y³+y²+24

3. Add (m+2n) from the difference of (3m-7n) and (2m+n).

Solution:

• (3m-7n)-(2m+n)
• 3m-n-2m-n
• 3m-2m-n-n
• m-2n

Now, add (m+2n) and (m-2n).

• (m+2n)+(m-2n)
• m+2n+m-2n
• m+m+2n-2n
• 2m

Answer: 2m

4. Subtract (40a³b²+21a²b³-13) from the sum of (30a³b²+10a²b³-17) and (20a³b²+12a²b³-16).

Solution:

• (30a³b²+10a²b³-17)+(20a³b²+12a²b³-16)
• 30a³b²+10a²b³-17+20a³b²+12a²b³-16
• 30a³b²+20a³b²+10a²b³+12a²b³-17-16
• 50a³b²+22a²b³-33

Now, subtract (40a³b²+21a²b³-13) and (50a³b²+22a²b³-33).

• (40a³b²+21a²b³-13)-(50a³b²+22a²b³-33)
• 40a³b²+21a²b³-13-50a³b²-22a²b³+33
• 40a³b²-50a³b²+21a²b³-22a²b³-13+33
• -10a³b²-a²b³+20

Answer: -10a³b²-a²b³+20