Answer:
His sister sent 6 more messages than Diego.
Step-by-step explanation:
Ratio of Diego's messages to his sister's messages = 3 : 4
Text messages sent by Diego = 18
Text messages sent by his sister = x
Ratio = 18 : x
It is a proportional relationship,
3 : 4 :: 18 : x
Product of extremes = Product of means
3x = 18*4
3x = 72
Difference = 24 - 18 = 6
Therefore,
His sister sent 6 more messages than Diego.