Ineed to know this answer i've worked it out but not sure

(r⁻³.s⁵.t²) / (r².s.t⁻²).
The easiest way to solve is to put the denominator on the numerator and to do so you just change the signs of the exponents:
denominator = (r².s.t⁻²), moving it to numerator it becomes: (r⁻².s⁻¹.t²), hence

(r⁻³.s⁵.t²) / (r².s.t⁻²).= (r⁻³.s⁵.t²)(r⁻².s⁻¹.t²) = r⁻³.s⁵.t².r⁻².s⁻¹.t²
a) r⁻³.r⁻²  = r⁻⁵
b) s⁵.s⁻¹ = s⁴
c) st².t² = t₄

Answer = r⁻⁵.s⁴.t⁴ OR s⁴.t⁴/r⁵ (answer B)