Resultant force questions help

Can someone please help me with these resultant force questions? I don't really know how to start and I'm getting really confused...

1. A block of mass 3kg is acted on by a force R=2i+5j in newtons. Calculate the magnitude and direction of the acceleration.

2. A uniform force acts on a box with a mass of 5kg and causes the box to accelerate at (4i+8j)m/s^-2. Find the magnitude and direction of the force acting on the box.

3. A body of mass 20kg is acted on by two forces, P=12i-4j and Q=20i+32j, where both forces are measured in newtons. Calculate the magnitude and direction of the acceleration.

Answers: 1. 1.8m/s^-2 at tan^-1(5/2) 2. 20√5 N at tan^-1(2) 3. 2.13m/s^-2 at tan^-1(7/8)

I don't really understand how to get to these answers, so any help will be greatly appreciated!!!!

1. You can calculate this in terms of the unit vectors or calculate a resultant force and direction. For the former method, since F = m*a, a = F / m:

a(i) = 2 N / 3 kg = 0.67 m/s^2.
a(j) = 5 N / 3 kg = 1.67 m/s^2

Resultant acceleration, a(r) = 0.67i + 1.67j m/s^2

For the latter method:
The resultant force, Fr = sqrt(2^2 + 5^2) = 5.39 N.
a = F / m
a = 5.39 N / 3 kg = 1.8 m/s^2. The direction with respect to the x-axis is arctan(5 / 2) = 68.2 degrees.

2. Solve each component of force:
F(i) = m * a(i) = 5 kg * 4 m/s^2 = 20 N
F(j) = 5 kg * 8 m/s^2 = 40 N.
F(r) = 20i + 40j N. = sqrt(20^2 + 40^2) = 44.7 N (=20 * sqrt(5)). Angle = arctan(40/20) = arctan(2) = 63.4 deg. (with respect to x-axis).

3. You can add forces in x and y directions to get the resultant force P + Q:

P + Q = (12i + 20i + (-4j) + 32j) N = 32i + 28j N. Then you calculate this the same way as problem 1.