Hello, 
Task 3: Fill half of the memory with one and other half with another colour
LDX #$00
loop:
	LDA #$1
	STA $200, X
	STA $300, X
	LDA #$2
	STA $400, X
	STA $500, X
	INX
	BNE loop 

Task 4: Store one 32 bit number in memory starting at $200, another at $210. Choose how to store the number yourselve. Add those numbers and store result in $220 
; Little indian 
LDA #$ff 
STA $200 
LDA #$44 
STA $201 
LDA #$44 
STA $202 
LDA #$44 
STA $203 

LDA #$01 
STA $210 
LDA #$44 
STA $211 
LDA #$45 
STA $212 
LDA #$44 
STA $213
 
LDA #$0 
LDX #$0 
CLC 
PHP 
loop: 
	PLP 
	ADC $200,X 
	ADC $210,X 
	PHP 
	STA $300,X 
	LDA #$0 
	INX 
	CPX #$4 
	BNE loop


Task 4: Create two dots in the middle of the „video memory”. Animate
them moving in oposite directions, first on X then on Y axis.
Repeat until reset.

define p1 $0
define p2 $1

define color $1

LDA #$ff
STA p1
LDA #$40
STA p2

main_loop:
  loop1:
    LDA p2
    CLC
    ADC #$ff
    STA p2
    TAX

    LDA #color
    STA $300,X
    LDA #0
    STA $301,X

    LDA p1
    CLC
    ADC #$1
    STA p1
    TAX

    LDA #color
    STA $300, X
    LDA #0
    STA $2FF, X

    CPX #$20
    BNE loop1
 
 LDA p1
 TAX
 LDA #0
 STA $300,X

 LDA p2
 TAX
 LDA $0
 STA $340,X

 LDA p1
 PHA
 LDA p2
 STA p1
 PLA
 STA P2
 
 JMP main_loop