Question

8/f = 56/105 what is f?

Answer 1

8/f= 56/105

Cross multiply:
56* f= 8*105
⇒ f= 8*105/56= 15

Final answer: f=15~

Answer 2

8/15 = 56/105

This may be solved using proportion.
a/b = c/d
ad = bc where cross products are equal.

a = 8
b = f
c = 56
d = 105

ad = bc
8*105 = f*56
840 = 56f
840/56 = 56f/56
f = 15

56 ÷ 7 = 8
105 ÷ 7 = 15