Answer: The correct answer is option C: 423 km
Step-by-step explanation: The triangle shows two sides given as 160km and 450km. However the angles facing those sides are yet unknown. Also the third side is unknown (marked x) but the angle facing line x is given as 70 degrees. These dimensions satisfies the requirements for applying the Cosine Rule which states that;
c^2 = a^2 + b^2 - 2abCosC
In this question we shall take line x to be c, while angle C is 70. Also a and b are 160 and 450 respectively. Hence
x^2 = 160^2 + 450^2 - 2(160 x450) Cos 70
x^2 = 25600 + 202500 - 2(72000) x 0.3420
x^2 = 228100 - (144000 x 0.3420)
x^2 = 228100 - 49249
x^2 = 178852
Add the square root sign to both sides of the equation
x = 422.908
Approximately to the nearest kilometer,
x = 423 km
The straight line distance from Monclova to Durango is 423 kilometers