This is a ratio problem, so it would/ should be set up as 35/28:d/40 or something similar to that. All you do to solve for variables in ratios, is just multiply the two diagonal numbers(the ratio looks different when you write it out) and then divide it by the remaining number. So you do 35 x 40 which equals 1400 and divide that by 28 so 1400/28=50 so d= 50. Hope this wasn’t too confusing! :)
