Question 45757
a=1/2h(a+b+c+d) solving for b

a=1/2ha +1/2hb +1/2hc +1/2hd

subtract 1/2hb from both sides

-1/2hb=1/2ha+1/hc+1/2hd

now seperation the -1/2 and h from the b by dividing out -1/2 h from both sides

and you end up with b all by it's self giving you

b=1/2ha + 1/2hc + 1/2hc /(divided by) -1/2h