decipher this modified sum operation,

This is crossposted from Math.SE, the original question is here

$1+2+3+4 = 61$

$2+3+4+5 = 52$

$3+4+5+6 = 51$

$4+5+6+7 = 50$

$7+8+9+10 = ?$

• Ugh, do you HAVE to use $+$ and $=$ for these? – Deusovi Jan 17 '16 at 6:50
• @Deusovi, why not? I think it is nicer this way. – klm123 Jan 17 '16 at 8:03