You can use the proportion.
$4.99 / 1 kg = x / 1.8 kg
x = ($4.99 * 1.8 kg) / 1 kg
x = $8.98
Therefore, in 1.8 kg of potatoes, it costs at $8.98
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You can look at -32 as being -2^5 so if you write (-2^5)^3/5 the 5's cancel out making it -2^3 which equals -8
158.71 rounded to the nearest ten dollars would be $160.00
then to estimate 10% since 10% starts with a 1, just remove the zero from both numbers
so 160 becomes 16
the tip would be $16
Assuming you meant 2+3(67x34)=y
67x34=2278
2+3(2278)=y
5(2278) or 5x2278=y
y=11390