Answer:
f = 1
Step-by-step explanation:
Use the method of cross- multiplication
[tex]\frac{a}{b}[/tex] = [tex]\frac{c}{d}[/tex] ⇒ ad = bc, thus
20f = 5(f + 3) ← distribute
20f = 5f + 15 ( subtract 5f from both sides )
15f = 15 ( divide both sides by 15 )
f = 1
