Question

candle 1's rate: 19.5 cm/hr
candle 2's rate: 0.15 in/min

1 inch = 2.54 cm
0.15 in = 0.15x2.54 = 0.381 cm

candle 2's converted rate = 0.381 cm/min
60 min = 1 hr
0.381 cm/min = 0.381x60 cm/hr = 22.86 cm/hr

compare:
Candle 1 @ 19.5 cm/hr
Candle 2 @ 22.86 cm/hr
===> Candle 1 melts more slowly so would be the preferred choice

Part B:
x-axis would be time, and each unit on the axis would be appropriate at 30 min.
y-axis would be height, with each unit being, perhaps, 4 cm so candle would start at (0,10)