Algebra 2 question

Question

Martina, Keith, and Deshaun sent a total of 11  text messages over their cell phones during the weekend. Deshaun sent 3 times as many messages as Keith. Keith sent 7 more messages than Martina. How many messages did they each send?

Answer 1

M+K+D = 11

D=3K

K=7+M

M+7+M+3(7+M) = 11

5M + 28 = 11

M = -17/5 = -3.4 = negative messages for Marina

K= 7-3.4 = 3.6 messages for Keith

D=3K = 3(3.6) = 10.8 messages for Deshawn

The problem has a negative and fractional numbers of messages, making it weird. Either the problem was not copied right, or the formulator of the problem was either miscalculating or insane.