check the picture below.
since coordinate for the height of each triangle, is pretty much the left-endpoint y-value, then the upper estimate will be
2(8.7) + 2(7.6) + 2(6.8) + 2(6.2) + 2(5.7)
2(8.7+7.6+6.8+6.2+5.7) => 70.
notice in the picture, that the last endpoint of 5.3, is not really a left-endpoint, so the height of the last rectangle is not 5.3, but 5.7.
