a+6+9.35+(2a+6+9.35)*.0715=261.76

Solution for a+6+9.35+(2a+6+9.35)*.0715=261.76 equation:

a+6+9.35+(2a+6+9.35)*.0715=261.76

We simplify the equation to the form, which is simple to understand 
a+6+9.35+(2a+6+9.35)*.0715=261.76

Reorder the terms in parentheses
a+6+9.35+(+1.097525 + 0.143a)=261.76

Remove unnecessary parentheses
+a+6+9.35+1.097525 + 0.143a=+261.76

We move all terms containing a to the left and all other terms to the right. 
+1a + 0.143a=+261.76-6-9.35-1.097525

We simplify left and right side of the equation. 
+1.143a=+245.312475

We divide both sides of the equation by 1.143 to get a. 
a=214.62158792651