What you will do is to use the rule of P.M.D.A.S (Parenthesis, Multiplication, Division, Addition, and Subtraction). This is a basic problem solving technique in computing long equations in math.
Since you equation is 3.26 + (-4) you will first look at the signs with the parenthesis. When you multiply a positive sign with a negative sign the result will always be negative. Translating that into an equation it looks like this:
+(-4) = - 4
Your new equation with the answer would then be:
3.26 - 4 = -0.74