For this question you take-off from an airfield at MSL - the
data they give you is the TOC stuff .... FL75 OAT +5°C .... the temperature is 'OUTSIDE
AIR TEMPERATURE', versus an ISA deviation .... (ISA +...)
When you use this graph, enter the first time at your TOC OAT ... +5°C in this instance .... IF you were taking off from an airfield that
was NOT at MSL, you would need to enter a second time to correct for that elevation .... the second time you
enter would be at AIRFIELD OAT, working up to AIRFIELD ELEVATION .... etc