They use 9 blocks each, a total of 18 blocks.
Bill: 4b + 2 b = 1.75 ; then, 4(1.75) + 2 = 7 + 2 = 9
Ron: 8b - 5 b = 1.75; then, 8(1.75) -5 = 14 - 5 = 9
To look for the value of b; I assume that both used the same number of blocks.
4b + 2 = 8b - 5
4b - 8b = -5 -2
-4b = -7
-4b/-4 = -7/-4
b = 1.75