Question 1196210
Let 
    A = number of Type A Trucks the grocer should rent
    B = number of Type B Trucks the grocer should rent

    C = total rental cost

The problem says:

    C = 30A + 40B           (1)

Given constraints
    20A + 15B > or = 3,000  (2)
    10A + 15B > or = 4,000  (3)
    A > or = 0, B > = 0

Subtracting equation (2) by (3) 
gives A = -100. Choose A =0.

With A = 0, calculate B.
Equation (3)
     15B > or = to 4,000
       B = 267

Answer: 
The grocer should rent 267 Type B Trucks only.