Answer:
3
Step-by-step explanation:
Numbers between 21 and 30 divisible by 3 are 24 and 27. so you get the HCF of the two.
 
        
             
        
        
        
Answer:
10^2+2×2b×10+2b^2 = 100+40b+2b^2
 
        
             
        
        
        
Answer: C. (-7x+9)(x-2)
Step-by-step explanation: 
1. Factor out the negative sign.
−(7x^2+5x−18)
2. Split the second term in 7x2+5x−18 into two terms.
−(7x^2+14x−9x−18)
3, Factor out common terms in the first two terms, then in the last two terms.
−(7x(x+2)−9(x+2))
4.  Factor out the common term x+2x+2x+2.
−(x+2)(7x−9) or (-7x+9)(x-2)