Don’t understand b) pls explain

Below in bold.

Step-by-step explanation:

-(s - t) - (s - t)^2       Take out  (s - t):

= (s - t)( -1 - (s - t)

= (s - t)(t - s - 1). <  Factored form.

Or, if you want to  expand the expression:

-(s - t) - (s - t)^2

= - s + t - (s^2 - 2st + t^2)

= -s^2 + 2st - t^2 - s + t.

7! = 7×6×5×4×3×2

3! = 3× 2

as 7! is multiple of 3! because 7! contains 3! that is 3× 2 as factor

so 7! /(3! ) = 7× 6× 5× 4

= 42 × 20

= 840

its b) 840✌✌✌

dhruv⭐

the answer to the expression is 83