Question 933108
let x = boys
    x+4= girls
    total= 30
equate:
     x+(x+4)=30
     x+x+4=30
      2x+4=30
        2x=30-4
        2x=26
         x=13

substitute x

x=13 boys
x+4=13+4=17 girls

add the no. of boys and girls will equal to 30