Help! Solve the following equation for h 1 over f equals 1 over d minus 1 over h

Question

Help! I know this is a basic question but i'm so stuck on it, 30 year old learning basic math here! 

Solve the following equation for h

1 over f = 1 over d - 1 over h

Answer 1

1/f=1/d-1/h to solve for h.

Multiply both sides by fdh:

dh=fh-fd, fd=fh-dh.

Take out the common factor h (that is, factorise the RHS):

fd=h(f-d), fd/(f-d)=h or h=fd/(f-d).

Another way:

1/f=1/d-1/h=(h-d)/dh.

Turn both sides upside down:

f=dh/(h-d), f(h-d)=dh, fh-fd=dh, fh-dh=fd.

Take out the common factor h:

h(f-d)=fd, h=fd/(f-d).