Tìm x thỏa mãn: 3/20 + 3/30 + 3/42 + 3/56 + ... + 3/x(x+1) = 18/25

Tìm x thỏa mãn:
a, 3/20 + 3/30 + 3/42 + 3/56 + ... + 3/x(x+1)=18/25
b,(x+1) + ( x+2 )+...+(x+2022)=2049297