Question 132726
Let x=weight of Pulse Jet
Then (x-20)=weight of Scramjet
And (x-20)+7=(x-13)=weight of Turbofan

Now we are told that:

x+(x-20)+(x-13)=1248  or
x+x-20+x-13=1248  simplify

3x-33=1248  add 33 to both sides
3x-33+33=1248+33  collect like terms
3x=1281  divide both sides by 3

x=427 kg--------------------weight of Pulse Jet
x-20=427-20=407 kg-------------------------weight of Scramjet

x-13=427-13=414 kg------------------------------weight of Turbofan

CK
427+407+414=1248
1248=1248


Hope this helps---ptaylor