This seems to be an equation where the sun is the variable and, therefore, you have to find the value of it. If this is true, isolate the sun at one side of the equation, passing the -10 to the other side of the <em>=</em> symbol with what is called "Inverse Operation".
Sol-10 = 11
Sol = 11+10
The -10, as is going to the other side of the equation, it passes with the opposite sign.
