Answer:
The triangle is acute.
Step-by-step explanation:
Basically, you need to use Pythagoras Theorem.
This is what you need to know then
In ABC with longest side c:
c²<a²+b² then the triangle is acute.
c²=a²+b² then the triangle is right.
c²>a²+b² then the triangle is obtuse.
So let´s go Pythagoras Theorem for your triangle.
4.2²=17.64
6.4²=40.96
7.6²=57.76
57.76<17.64+40.96
So the triangle is acute
