Avg. speed Joanna runs: 7.5km/h
how much she runs everyday: 15km
15km/7.5= 2 hours of running time everyday
She leaves at 8:30, comes back at ?
8:30+ 2:00= 10:30
Joanna arrives back at 10:30a.m.

Because the denominators are same, you can just add the numerators.
Four million, three hundred, fifty thousand, seven hundred, sixty-two
2=10
3 =15
7=35
1=5
Constant of 1 is 5
You can use the Law of Cosines, if only one of which is missing: three sides and one angle. Hence, if the known properties of the triangle is SSS(side-side-side) or SAS (side-angle-side), this law is applicable.
You can use the Law of Sines if you want to equate the ratio of the sine of an angle and its opposite side. This can be used if the known properties of the triangle is ASA(angle-side-angle) or SAS.
The ambiguous case is the SAS triangle. This could be easily solved using Law of Sines than Law of Cosines. Take for example: side a = 4, side b = 10, angle A = 23°. Then, we can determine angle B through Sine Law.
sin 23°/4 = sin B/10
B = 77.64°