$C= 2.3+3.4+4.5+...........+60.61^{}$
$3C=2.3.4+3.4.4+4.5.4+...........+60.61.4^{}$
$3C=2.3.(4-0)+3.4.(5-1)+4.5.(6-2)+...........+60.61.(62-58)^{}$
$3C=2.3.4 - 1.2.3+3.4.5-1.2.3+4.5.6-2.3.4+...........-58.59.60+60.61.62-58.59.60^{}$
$3C=60.61.62 - 1.2.3^{}$
$3C=226914^{}$
$C=226914÷3^{}$
$⇒C=75638^{}$