Answer:
x = 5.4
Step-by-step explanation:
The marked sides are the hypotenuse and the side adjacent to the marked angle. That suggests the appropriate trig function is the cosine:
Cos = Adjacent/Hypotenuse
cos(19°) = 5.1/x
x = 5.1/cos(19°) . . . . . multiply by x/cos(19°)
x ≈ 5.4
