Answer:
C 14n - 8
Step-by-step explanation:
rectangle area = length×width = 12n²-19n-21
width = 3n-7
what do we need to multiply with width to get the full area expression ?
think : what do we need to multiply with 3n to get 12n² (4n)?
and what to multiply with -7 to get -21 (3)?
=> length = 4n+3
perimeter is 2×length + 2×width
p = 2(3n-7) + 2(4n+3) = 6n-14+8n+6 = 14n-8
