Given, C1+C2+C3+C4=30
Now it has given that 4\leq {C}_{2}\leq 7&2\leq {C}_{3}\leq 6
and {C}_{1}&{C}_{4} can take any value.
Finding coefficient of x30 in
(x0+x1+......x30)(x4+x5+......x7)(x2+...x6)(x0+....x30)
=(1−x1−x31)2x4(1−x1−x4)x2(1−x1−x5)
{Ignoring higher power more than 30}
=(1−x1)2x4(1−x1−x4)x2(1−x1−x5)
=x6(1−x4)(1−x5)(1−x)−4 =x6(1−x5−x4+x9)(1−x)−4
=(x6−x11−x10+x15)(1−x)−4
Required coefficient =C244+24−1−C194+19−1 −C2020+4−1+C1515+4−1
=C2427−C1922−C2023+C1518 =430