remember you can do anything to an equation as long as you do it to both sides
pemdas
first, subsitue z for the blank
(4z)-(1+8x2)=3
simplify
(4z)-(1+16)=3
(4z)-(17)=3
4z-17=3
add 17 to both sides
4z+17-17=3+17
4z+0=20
4z=20
divide both sides by 4
4z/4=20/4
1z=5
z=5
the blank is 5