A(3)=4+(3+1)(-5)

Solution for A(3)=4+(3+1)(-5) equation:

a(3)=4+(3+1)(-5)

We simplify the equation to the form, which is simple to understand 
a(3)=4+(3+1)*(-5)

Simplifying terms in parentheses
a*(3)=4+(+4)*(-5)

Reorder the terms in parentheses
+(+3a)=4+(+4)*(-5)

Remove unnecessary parentheses
+3a=+4+(+4+)+*(-5+)

Reorder the terms in parentheses
multiplication of parentheses
+3a=4+(-20)



Remove unnecessary parentheses
+3a=+4-20

We move all terms containing a to the left and all other terms to the right. 
+3a=+4-20

We simplify left and right side of the equation. 
+3a=-16

We divide both sides of the equation by 3 to get a. 
a=-5.33333333333