#1
5*3/5+7*4/7=3+4=7
4/7*5+3/5*7=20/7+21/5=100/35+147/35=247/35=7 2/35
#2
(7b+3a)+(8b-5a)-10b+2a=7b+3a+8b-5a-10b+2a=5b
8a+(3a-2)-(5a-2)=8a+3a-2-5a+2=6a
7+2(3x-4)=7+6x-8=6x-1
#3
15/x=12/8
15*8=12x
-12x=-120:(-12)
x=10
(-2x+1)/4=(-2-3x)/5|*20
-10x+5=-8-12x
-10x+12x=-8-5
2x=-13:2
x=-6,5
#4
11x+x-3x-5x+6x=10x=25,4*10=254
-5b-4(0,8-b)+2,3=-5b-3,2+4b+2,3=-b-0,9=-0,3-0,9=-1,2
#5
P=2a+2b
2b+(b+7)*2
2b+7b*2