Explanation:
for % questions always find 100% and/or 1%.
everything else can be easily calculated out of these 2.
the original price of $210 = 100%, as we want to know how many % the new price is different from that.
100% = $210
1% = 100%/100 = 210/100 = $2.10
the new price is $300.
the difference is 300 - 210 = $90
how many % are $90 compared to the original price ?
well, as many as the times 2.1 (1%) fits into 90 :
90/2.1 = 42.85714286...%
that increase from $210 to $300 was 42.85714286...%.
an additional $50 baggage fee ?
we have to add this to the $300 and get $350 as new price.
that difference is now 350 - 210 = $140.
how many % are $140 compared to the original price ?
140/2.1 = 66.66666666...%
that increase from $210 to $350 was 66.66666666...%.