answer
1.7 ≈ x
reasoning
first find the missing value of the triangle on the bottom
6^2 + 5^2 = c^2
36 + 25 = c^2
61 = c^2
sqrt61 = c
then use that to find x
(sqrt61)^2 + b^2 = 8^2
61 + b^2 = 64
(61 + b^2) - 61 = 64 - 61
b^2 = 3
sqrt(b^2) = sqrt3
sqrt3 = b
1.7 ≈ b