What is the perimeter of a triangle with sides of lengths 5, 8, & x? a.13 + x b.40 + x c.40x d.21

The perimeter of a triangle can be found by adding up all the sides

so the perimeter is : 
5 + 8 + x =
13 + x <==

This is what i found “an explicit formula designates the nth term of the sequence, as an expression of n (where n = the term's location). it defines the sequence as a formula in terms of n. this example is an arithmetic sequence(the same number, 5, is added to each term to get to the next term).” i hope this you for what your looking for. can you plz mark me brainliest?

Xis equal to three