Question 44105
1.4r^3-4 
=4(r^3-1)
=4(r-1)(r^2+r+1)

2.(21-7t)+(3r-rt)
=7(3-t)+r(3-t)
(3-t)(7+r)
 
3.x^3+64y^3
=(x+4y)(x^2+4xy+16y^2)
 
4.(x^3+7x^2)+(-4x-28)
=(x^2)(x+7)-4(x+7)
=(x+7))(x^2-4)
=(x+7)(x-2)(x+2)

Cheers,
Stan H.