2b=2

2b/2=2/2

b=1

5b+2u = 13

5(1)+2u = 13

5+2u = 13

5+2u-5 = 13-5

2u=8

2u/2=8/2

u=4

b+2u+3y = 24

1+2(4)+3y = 24

1+8+3y = 24

9+3y = 24

9+3y-9 = 24-9

3y=15

3y/3=15/3

y=5