Two years older than my age at that time means: when my sister grows up to my sister's age, Ms. Liu's age. Let my sister be X and Y, and my sister is (x-y) years older than my sister. It was (x-y) years when my sister grew up to Y. At this time, my sister's age is x+(x-y)=2x-y, and Ms. Liu's age is 48+(x-y). At this point, the total age of the two sisters is x+(2x-y), so the formula should be:

X+(2x-y)=48+(x-y)+2, and only X is left in simplification, so x=25. It should be detailed enough. This problem is derived step by step, and it is not difficult.