Question 23556
representing x is the units, y is the tens and z is the hundreds.

eq#1 x+y+z=19
eq#2 z=3y
since "The number is 198 more than the number reversed"
 so 
Eq#3 100z + 10y + x=100x+10y+z+198
simplify,z-u=198  <divisible by 99>
you may use substitution but it'll make your solution very long so, use elimination. 

eliminate eq.1  and 3
then substitute.