Answer:
b =15
Step-by-step explanation:
The sum of the angles of a triangle is 180
5b+ 4b+ 3b = 180
12b = 180
Divide by 12
12b/12 =180/12
angles in a triangle add up to 180
so 5b+4b+3b=180
simplifed is 12b=180
so b=15
