If you mean find side b which is opposite to angle B then by using the sine rule:

3*sin(17)/sin(56) = 1.058 rounded to 3 decimal places

Given side a = 3, angle A = 56° and angle B = 17°, find side b?    

Obtuse scalene triangle:

b = 1.058 

Law of Sines: b/sinA = a/sinA

b = a·sinB/sinA

 = 3sin(17°)/sin(56°)

 ≅ 1.058 units

:-

b / sin B = a / sin A

b = a sin B / sin A

b = 3 sin 17° / sin 56°

b = 1•06

Sine rule...

a/sin A = b/sin B

b = a.sinB/sinA

b = 3 x sin 17/sin 56

b = 1.05