Put the first equation into y= mx + b form: 
5x + 20y = 10 
Subtract 5x from both sides: 
20y = 10 - 5x 
Divide both sides by 20:
y = 1/2 - (1/4)x 
y = -(1/4)x + 1/2 
This means -1/4 is your slope. To be parallel, the new equation must have the same slope. 
Start with: y = -(1/4)x + b
Plug in 8 for the x and the 3 for the y: 
3 = -(1/4)(8) + b 
3 = -2 + b 
Add the 2 to both sides: 
5 = b 
Your answer is: 
y = -(1/4)x + 5