Answer:
Each of them eat 140 scoops.
Step-by-step explanation:
Let x be the amount eaten by each of them,
Given,
The initial ice cream Masha has =  200 scoops
Final ice cream Masha has = ( 200 - x ) scoops
while the initial ice cream Liz has = 180 scoops,
Final ice cream Liz has = (180-x) scoops,
According to the question,

 ( by cross multiplication )
 ( by cross multiplication )
 ( Subtracting 400 on both sides )
       ( Subtracting 400 on both sides )
 ( adding 3x on both sides )
  ( adding 3x on both sides )
Hence, each of them eat 140 scoops.