Given that Dan borrowed $1,250.00 from his brother who is charging him 5% simple interest. Now we have to find the total payment that he needs to payback including interest. Hence we can use simple interest formula
I=PRT
Where P= 1250
R=5% =0.05
T=18 months = 18/12 = 1.5 years
Now plug these values into above formula
I=PRT=1250*0.05*1.5=93.75
So total payment including interest = 1250+93.75=1343.75
Hence final answer is $1343.75.