Answer:
19
Step-by-step explanation:
-9b -5 -7b = -309
-16b - 5 = -309
16b = 309 - 5
16b = 304
b = 304 ÷ 16
b = 19
hi
pen = 12
book = 24
x = cost of pen
2x + x = 36
3x = 36
x = 12
