Question 332982
Let x b ethe daily wages and y be the commission percentage
first we have to form two equations and find x and y 
he sells $500 worth of merchandise in one month, he is paid $410
ie;
daily wages +commission rate of 500 =$410
x+y%of$500=$410
x+y/100*500 =$410
x+5y=$410 ------------------(1) 
he sells $900 of merchandise in one month, he is paid $498
x+y%of$900 =$498
x+y/100*900=$498
x+9y=$498------------------(2)
from (1) and (2)
x+5y=410
x+9y=498
________________
(1)-(2) =-4y=-88
y=22
x+5y=410
x+5*22=410
x=410-110=300
so the commison rate is 22% and daily wages is $300
Justins salary when he sells $3,400worth of merchandise is
x+y%of 3,400
=300+22%*3400
300+22*3400/100
300+22*34
=300+748 =$1048
Justines salary when he sells $3,400 is $1,048