let

h = the age of Huilan

t = the age of Thomas

Huilan is 15 years older than Thomas:

h = t + 15

The sum of their ages is 93:

h + t = 93

by solving the system of equations:

h = t + 15

h + t = 93

we find:

h = 54 years

t = 39 years

click here to see the step by step solution of the system of equations:

Thomas is 39 years of age.