Tips for the "Rate Problems 2" Practice.

I dont know if this belongs here but I feel like the Rate Problems 2 Exercises could be better explained. (Located in Algebra 1 -> Working With Units -> Rate Problems 2). See attached for an example problem. 

I feel like my way (not really my way but one found using external resources) could be better at explaining whats going on. Imo, they currently dont really use the rate formula...er....formulaically....and leading to difficulty applying it to the problems and in other situations. 

It takes 32 minutes for 3 people to paint 4 walls. How many minutes does it take 4 people to paint 7 walls?

Here we basically have an "equal" rate problem, R1 = R2 with our units being w/pm or walls per people-minutes.

The first rate is R1 = (Amount 1) / (Time 1)...ie. (4 walls) /  (3 people) * (32 min) = 4w / 3p * 32m

The seond rate is R2 = (Amount 2) / (Time 2)...ie. (7 walls) / (4 people) (X min ) = 7w / 4p * Xm.

From here on out the math is pretty simple:

R1 = R2 

(4 walls) / [(3 people) * (32 min)] = (7 walls) /  [(4 people) * (X min)]

(4w) / (3p) * (32m) = (7w) / (4p) * (Xm)

(4w) * (4p) * (Xm) = (7w) * (3p) * (32m)

solve for X

(16wp * Xm) = (21 wp * 32m)

Xm = (672pwm) / (16pw)

Xm =42m

This is good (imo) for 3 reasons....1) It uses the logic of the Rate Formula, 2) It helps us identify that we need to multiply the number of minutes by each person to get the TOTAL time for the rate to apply to our Rate Formula and 3) it helps us identify our units which is a previous topic (Appropriate units) and be able to cancel them out.

The hints arnt wrong....just not as useful in learning how to apply the rate formula....imo. The solutions provided just kinda wing it by "feel." Maybe thats whats intended. I dont know. Let me know what others think.