#### Answer

a. $C=5.29(x) + 400$
b. 929 dollars
c. 160 proofs

#### Work Step by Step

a. $x=number of proofs$
$C=cost$
$C=5.29(x) + 400$
b. $C=5.29(100) +400$
$C=529+400$
$C=929$
c. $C=1250$
$1250=5.29(x)+400$
$1250-400=5.29(x)$
$850=5.29(x)$
$850\div5.29=x$
$x=160.68$
$x=160$