Ok, here's the full table I was given:
Y1 = 10.1cm, X1 = 15g,,, t1 = 3.306 months
Y2 = 25.0cm, X2 = 236g,, t2 = 9.179 months
Y3 = 32.0cm, X3 = 520g,, t3 = 12.513 months
Y4 = 35.4cm, X4 = 660g,, t4 = 14.313 months
Y5 = 43.8cm, X5 = 1250g, t5 = 19.425 months
Y6 = 45.5cm, X6 = 1425g...