Answer:The length of the third side 2.5.
Step-by-step explanation:
We already know the length of two side but we don’t know the length of one side so we will represent it by b and we know they three lengths add up to 12b+5.
4b + 3b+15 +b =12b + 5
Solve for b.
8b +15=12b +5
-8b -8b
15+4b +5
-5 -5
4b/4=10/4
B=2.5
So the length of the third side is 2.5
4(2.5) + 3(2.5)+15+2.5=12(2.5)+5
35=35