If 1/f= 1/u+1/v , make f the subject of the formula.
help pl.

f = uv/ (v+u)

Step-by-step explanation:

1/f= 1/u+1/v

Multiply each side by fuv to clear the fractions

fuv( 1/f)= fuv(1/u+1/v)

uv = fv+ uf

Factor out the f on the right hand side

uv = f(v+u)

Divide each side by (v+u)

uv/ (v+u) = f(v+u)/ (v+u)

uv/ (v+u) = f

f=uv/(v-u)

Step-by-step explanation:

1/f=1/u + 1/v

1/f=(v-u)/uv

Cross multiplying we get

uv=f(v-u)

Divide both sides by (v-u)

uv/(v-u)=f(v-u)/(v-u)

uv/(v-u)=f

Therefore f=uv/(v-u)

answer is:

1.75 pounds

i think it would be 42cm