Hi,
Let's solve for x. 
y= 3 /8 (x+4) 
Step 1: Flip the equation. 
3/8x +3/2 =y 
Step 2: Add (-3)/2 to both sides. 
3/8x + 3/2+ −3/2 =y+ −3/2 3/8 x = y+ −3/2 
Step 3: Divide both sides by 3/8. 
3/8x / 3/8 = y+ −3/2/3/8 
x= 8y−12/3
Answer: 
x= 8y−12/3 
Have a great day!