The sum of a number times 2 and 19 is at least -27. use variable b for unknown number.

Sum means add
sum of twice a number and 19 means 2b+19
at least means greater than or equal to

2b+19≥-27
to solve
minus 19 both sides
2b≥-46
divide both sides by 2
b≥-23
de number is at least -23

Okay, so lets break this down.

Lets use b for the number since it says that you need to.

So the sum of a number times two (2n) and 19 can be shown as 2b+19 ≥ -27.  Then, you subtract 19 from both sides and end up with 2b ≥ -46.  Then divide by 2 on both sides and you get b ≥ -23.

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Step-by-step explanation:

if Serina needs t=0.25 hours to drive to school, which is s=16 km away

her speed is

v= s/t    t=0.25h

v=16 km/15 min or v= 64 km/h ( multiply by 4 to get 1 hour)