Question

Can someone explain? Please help! 15 pts!!!!

Answer 1

Let 
x--------------> the third stone measure

we know that
the recommended height for the bench is ------> 20 in
20=[4 3/8]+[4 1/2]+[5 1/4]+[x]
4 3/8---------> (4*8+3)/8=35/8
4 1/2---------> (4*2+1)/2=9/2
5 1/4---------> (5*4+1)/4=21/4

20=[35/8]+[9/2]+[21/4]+[x]

x=20-(35/8)-(9/2)-(21/4)

x=20-(35+4*9+2*21)/8-----> 20-113/8------- > (8*20-113)/8

x=47/8---------- > 5.875=5 7/8

the answer is 5 7/8 in