I just need help solveing this for class

Question

the perimeter of a triangle is 42 inches.one side measures 18 inches.The shortest side measures x inches. the longest side measures 1 inch less than four times the length of the shortest side. Write and solve an equation to find the length of the longest side. the is problem question

Answer 1

L = 4x -1

L+x = 42 -18 = 24

4x-1 + x = 5x-1 = 24

5x = 25

x = 5 inches = the shortest side

L=4(5)-1 = 19 inches = longest side

3rd side = 18 inches

18+19+5 = 42 inches = perimeter