how would you solve for x? can you explain step by step?

40 = [(x+2.8)/2]*8.5

40 = [(x+2.8)/2]*8.5

multiply both sides by 2 to remove the 2 in the denominator.
40*2 = 2*[(x+2.8)/2]*8.5
80 = (x+2.8)*8.5
remove parentheses on right side by multiplying by 8.5.
80 = 8.5x + 2.8*8.5
80 = 8.5x + 23.8
move 23.8 to left side.
80-23.8 = 8.5 x
combine terms on left.
56.2 = 8.5x
divide both sides by 8.5
56.2/8.5 = 8.5x/8.5
6.61176 = x
Check my work.
Check it also by substituting the value of x into the original equation and see if the right side = 40.