I believe the answer would be 6.70820393 or ≈ 6.7 depending on how many decimal points you can put in.
So a^2+b^2 = c^2
In this case you are trying to find b
2^2+b^2 = 7^2
4 + b^2 = 49
B^2 = 45
b = the square root of 45
That is 6.70820393 or ≈ 6.7
Then see if it makes sense
2^2 + 6.7^2 = c^2
2(2) = 4
6.7(6.7) ≈ 45 (44.89)
———————-
49
And the square root of 49 is 7
Please correct me if I am wrong and have a good day