You can apply the Pythagorean theorem:
a^2 + b^2 = c^2
c is the longest side of the triangle
2.2^2 + 4.2^2 = 6.7^2
4.84 + 17.64 = 44.89
22.48 =/= 44.89
That is not a right triangle
Yes, but your answer will be a decimal, but make sure you check your work and one way you can check your work is by first combing like terms, and then solve it as it is an equation.