The area of a square poster is 59 in.2. Find the length of one side of the poster to the nearest tenth of an inch The length of one side of the poster is in.
(Round to the nearest tenth as needed.)

To solve this we can use the following system of equations: 
6a + 4c = 1326 
a + c = 289 
When a = adults and c = children. 
First we can take the second equation and subtract a from both sides to get  
c = 289 - a. Then substitute that into the first equation to get  
6a + 1156 - 4a = 1326. Next combine like terms to get 2a + 1156 = 1326. 
Now subtract 1156 from both sides to get 2a = 170. To get the final answer for a divide both sides by 2 to get a = 85. 
To get the value for c, now substitute it into the second equation to get 
85 + c = 289. Subtract 85 from both sides to get c = 201. 
85 adults and 201 children went swimming that day. Hope this helps!