The formula is given. b₁ and b₂ are the bases, (parallel top and bottom lines) add those together 18 +24 =42 then divide by 2 (that gives the average width) 42/2 = 21
7/8 / 2/5 is equal to 7/8 x 5/2 which equals 35/16, 16 goes into 35 twice so there are 2 wholes there is a remaining of 3 so we put it as a fraction over 16 the answer is 2 3/16
