Ok, so I'll assume you're using the United States fluid system, which has 32 fluid ounces in a quart. Add the amounts of fluid together, 144+24+56=224. Now divide by 32, which is the number of ounces in a quart:
224/32=7
In total, there are 7 quarts in the final mixture.
You're single equation would look like this:
(144+24+56)/32
