B and C are both correct
t(s) is equivalent to the temperature of the tea after s amount of seconds
3 (k-12) = k-30
3k - 36 = k - 30
3k - k = -30 + 36
2k = 6
k = 3
length = 1/2 w+9
perimeter= 60 =2(l+w)
substitute in for length
60 = 2(1/2 w +9 +w)
60 = 2 (3/2 w +9)
distribute
60 = 3w + 18
subtract 18 from each side
42 = 3w
divide by 3 on each side
14 = w
length = 1/2 w + 9
length = 1/2 (14) +9
7 + 9
16cm
