Answer:
Hey there! here's your answer
Step-by-step explanation:
Speed = distance/Time
Speed = 3/5 ÷ 1/2
Speed = 3/5 * 2
Speed = 6/5 mph or 1.2 mph.
2x+3 is the answer.................................................................

Hope you could get an idea from here.
Doubt clarification - use comment section.
Step-by-step explanation:
From the statement:
M: is total to be memorized
A(t): the amount memorized.
The key issue is translate this statement as equation "rate at which a subject is memorized is assumed to be proportional to the amount that is left to be memorized"
memorizing rate is
.
the amount that is left to be memorized can be expressed as the total minus the amount memorized, that is
.
So we can write

And that would be the differential equation for A(t).
2.8a^2=55
a^2=55/2.8
a= square root of 55/2.8