Start by defining your variables
let x be the mass of a single mango in gm
let y be the mass of a single orange in gm
now, write the question as a system of equations
3 mango and 2 orange have a mass of 200 gm
3x +2y = 200
4 mango and 4 orange have a mass of 300 gm
4x +4y = 300
now you have a system of equations
3x+2y =200
4x+4y =300
solve for x and y
You have to get X all by itself so you divide 20 and 30 which gives you a fraction. X= 20/30
Then = 2/3
It is a constant. hope this helps