Question 147265
A: [18x^4(y^3)]/[24x^2(y^3)]
Looking at the 18/24, it can be reduced to 3/4:
[3x^4(y^3)]/[4x^2(y^3)]
expand the x's:
[3xxxx(y^3)]/[4xx(y^3)]
each x on the denominator can be canceled with one on the top:
[3xx(y^3)]/[4(y^3)]
[3x^2(y^3)]/[4(y^3)]
expand y's:
[3x^2(yyy)]/[4(yyy)]
all the y's can be canceled:
[3x^2]/[4]
.

B: (4r^2-25s^2)/(2r^2+3rs-20s^2)
Check whether you have a typo, should it be:
(4r^2-25s^2)/(2r^2+2rs-20s^2)
factoring the numerator:
[(2r+5s)(2r-5s)]/(2r^2+2rs-20s^2)
factoring the denominator:
[(2r+5s)(2r-5s)]/[(2r-4s)(2r+5s)]
the 2r+5s cancel, leaving:
(2r-5s)/(2r-4s)