The applied examples in Muhammad ibn Musa al-Khwarizmi's Al-jabr wa'l muqabalah (The Compendious Book on Calculation by Completion and Balancing), the oldest book we have on algebra, are mainly business and inheritance.

A simple problem of interest to merchants:

Ten for six, how many for four?

and a similar problem on wages:

A man is hired to work in a vineyard 30 days for 10 pence. He works six days. How much of the agreed price should he receive?

The main focus for the applied problems is inheritance. For example:

A woman dies, leaving her husband, a son and three daughters.

The inheritance rules are complicated: in this case, the husband receives 1/4 of the estate, and each son receives twice as much as each daughter. These problems are well suited to algebra, since the more complex problems are beyond simple arithmetic (al-Khwarizmi doesn't bother with those problems), but can be readily solved with algebra.

For a discussion of the inheritance problems in Al-jabr, see Gandz (1938).

References:

Gandz, S. (1938), "The Algebra of Inheritance: A Rehabilitation of Al-Khuwarizmi", Osiris, 5, 319-391. http://www.jstor.org/stable/301569

The first two quotes above are from the English translation of Robert of Chester's Latin translation, from Louis Charles Karpinski, Robert of Chester's Latin translation of the Algebra of al-Khowarizmi, Macmillan, 1915, https://archive.org/details/robertofchesters00muha/