Y-intercept 4 mean that your line pases through (0;4)
  
 Your formula is:
 \(y=mx+b\)
  
 So we have (x;y) which is (0;4) and slope which is m=-2
  
 Let s put it into our formula:
 4=-2*0+b
 b=4
  
 Your equation:
 \(y=-2x+4\)
  
 Here s your graph:
 https://www.desmos.com/calculator/cjyxjbsaft