The fist box would be 40 and the second box would be 10. If you change 4/10 to have the same denominator as 100 it is 40 over 100. and if you say 8 is over 10 then it is 80 / 100. And 80 - 40 = 40, so it is 40.
176 rounds up to 180 17 rounds up to 20 The fact we're rounding up both times means we'll have an overestimate estimate = 180*20 = 3600 actual result = 176*17 = 2992
