3. (8 points) Longteng Primary School Grade 5 has four classes. Class 5-1 has 42 students, Class 5-2 is $\frac{6}{7}$ of Class 5-1, Class 5-3 is $\frac{5}{6}$ of Class 5-2, and Class 5-4 is 1.2 times the number of students in Class 5-3. The total number of students in Grade 5 is.
【Answer】Solution: Class 2: $42 \times \frac{6}{7}=36$ (people) Class 3: $36 \times \frac{5}{6}=30$ (people)

Class 4: $30 \times 1.2=36$ (people)
$$
42+36+30+36=144 \text { (people) }
$$

Answer: There are 144 people in Grade 5.
Therefore, the answer is: 144.