3/8 = .375 so we want .375 of $5460.40 or .375 x $5460.40 = $2047.65 savings
To find the checking we simply subtract:
$5460.40 - 2047.65 = $3412.75 - checking
You could also do 5/8 or .625 x $5460.40 to get $3412.75
because 3/8 + 5/8 (or .375+.625) = 1 (1 whole amount to save - in this case $5460.40)