What is the product?
(–3s + 2t)(4s – t)

Distributive property or
use FOIL (FOIL is just an acronym to help you remember how to multiply binomials)

distributive property
a(b+c)=ab+ac
(b+c)a=ba+ca

distribute
(-3s+2t)(4s-t)=
(-3s+2t)(4s)+(-3s+2t)(-t)=
(-3s)(4s)+(2t)(4s)+(-3s)(-t)+(2t)(-t)=
-12s^2+8st+3st-2t^2=
-12s^2-2t^2+11st

if you want foil

FOIL (just tells wich terms to multiply)
First
Outer
Inner
Last

exmaple
with
(a+b)(c+d)
First: a times c
Outer: a times d
Inner: b times c
Last: b times d
then add them

(-3s+2t)(4s-t)
First: -3s times 4s=-12s^2
Inner: 2t times 4s=8st
Outer: -3s times -t=3st
Last: 2t times -t=-2t^2

add them
-12s^2+8st+3st-2t^2=
-12s^2+11st-2t^2

same