Equation 10.5-2x = 2.1

Equation 10.5-2x = 2.1

How to do 10.5-2x = 2.1? Use the method of equation in Grade 5 of primary school
2x=10.5-2.1;
2x=8.4;
x=4.2;
I'm very glad to answer your questions. Skyhunter 002 will answer your questions
If you don't understand this question, you can ask,

My mathematics has degenerated. I want to start all over again and see which Equations I can't turn around. I want to ask you to find some equation solutions. For example, 13X + 9x = 33.3, I can't solve them,
13x+2x=33.3
22.2x/22.2=33.3
x=15
Wrong, it's 1.5 --

13x+9x=33.3
(13+9)x=33.3
21x=33.3
x=33.3÷21
x=1.59