Answer: $1398
Step-by-step explanation:
Given , Principal (P) = $12,500
Rate of interest for 1st year
= 12% =0.12
Rate of interest for 2nd year
= 15% =0.15
Rate of interest for 3rd year
= 18% =0.18
Interest for first year = 
= 
= $1500
Now, For second year new principal 
Interest for second year = 
= 
= $2100
Now, For third year new principal 
Interest for third year = 
= 
= $2898
Difference between the compound interest of the first year and the compound interest for the third year. = $2898 - $1500 = $1398
Hence, the difference between the compound interest of the first year and the compound interest for the third year is <u>$1398 .</u>