+1348 Find the coefficient of y^4 in the expansion of (2y - 5)*(5y - 2)^6.
+6 (2y - 5) * (5y - 2)^6....expand
= (2y - 5) * (15625y^6 - 37500y^5 + 37500y^4 - 20000y^3 + 6000y^2 - 960y + 64)
= 31250^7 - 153125y^6 + 262500y^5 - 227500y^4 + 112000y^3 - 31920y^2 + 4928y - 320
the coefficient of y^4 is: -227500
