Mark and Don have to sell 11 and 59 marbles respectively.
Explanation
Lets assume, the number of marbles Mark has is [tex]x[/tex]
As, Don has 4 more than 5 times the number of marbles mark has, so the number of marbles Don has [tex]= 5x+ 4[/tex]
Question says that the total number of marbles is 70. So, the equation will be...
[tex]x+(5x+4)= 70\\ \\ 6x+4= 70 \\ \\ 6x = 70-4\\ \\ 6x=66 \\ \\ x= \frac{66}{6}= 11[/tex]
So, the number of marbles Mark has = 11
and the number of marbles Don has = [tex](5*11)+4 = 55+4= 59[/tex]