a3=4
a9=22
a3=a1+2d
a9= a1+8d
a1=4-2d
a1=22-8d
4-2d=22-8d
6d=18
d=3
a1= 4-6= -2
a2021= a1+2020d= -2+2020*3= 6058
A) 100x-5=100
100x=105
x=105/100=1,05
Б) 5^2=3х-2
25=3х-2
3х=27
х=9