Help me please.

Question

A baker baked 450 donuts and buns. The number of donuts was 3/5 of the total number of donuts and buns. He sold some buns and the number of donuts became 9/13 of the total number of donuts and buns. How many buns were sold?

Answer 1

d+b=450

d=(3/5)450 = 270 donuts

buns = 450-270 = 180 buns

after selling some buns =x, then d=270= (9/13) of the total d+b left: 450-x

270 = 9(450)/13 -9x/13

multiply by 13 to eliminate fractions

270(13) = 4050 -9x

3510=4050-9x

9x = 4050-3510 = 540

x = 540/9 = 60 buns sold

he sold 60 buns leaving 450-60 = 390 total buns and donuts

270 = 9/13 times 390

13(270) = 9(390)

3510 = 3510