We are told that the height of the ballon after t seconds is given by the equation
[tex]\text{height}=120+2t[/tex]
and we are asked to find the height after 15 seconds.
To answer this question we simply put in t =15 in the above formula to get
[tex]\text{height}=120+2(15)[/tex]
This gives
[tex]\text{height}=120+30[/tex][tex]\text{height}=150m[/tex]
Hence, the height of the ballon after 15 s is 150m
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