I got the answer Antonio had a head start of 3 meters.
A product is the answer that you get when you multiply numbers together. So for this problem, you have 2 groups to multiply together. Since I cannot show a square or cubed x, I will put an x2 for x squared and an x3 for x cubed. You have to multiply each number in the first parentheses by each number in the second parentheses. Then combine any like sets.
(8x-3)(x2-4x+8)
8x3-32x2+64x-6x+12x-24
8x3-32x2+70x-24
So the answer is 8x cubed minus 32x squared plus 70x minus 24. Whew! That's a long one. Hope I didn't miss anything.
Assume r= t not sure if you mistyped this.
t = 15 min
T(t) = 68 (0.5)^(15/10) = 24 Celsius
31 = (0.5)^(t/10) take ln
ln31 = (t/10) ln (0.5) + ln68
t = (ln32 - ln 68/ln0.5) * 10 = 11.3 min
Suzy makes 675
Katie makes 500
Janine makes 800