a = numarul total de ore
I zi = a/4
II zi = 2/5 (a-a/4) = 2/5 x 3a/4 = 6a/20
a/4 + 6a/20 + 225 = a / x20
5a + 6a + 4500 = 20a
11a + 4500 = 20a
4500 = 9 a
a = 4500 : 9
a = 500
a) 500 ore s-au incarcat in cele 3 zile
b) 500 : 4 = 125 ore s-au incarcat a doua zi