a) -57.11 = -57(10+1) = -57.10 - 57 = -570 - 57 = -627
b) 75.(-21) = 75(-10-10-1) = -750 - 750 - 75 = -1500 - 75 = -1575
a) \(-57.11\)
\(=-57\left(10+1\right)\)
\(=-57.10+\left(-57\right).1\)
\(=-570+\left(-57\right)\)
\(=-627\)
b) \(75.\left(-21\right)\)
\(=75.\left[\left(-20\right)+\left(-1\right)\right]\)
\(=-1500+\left(-75\right)\)
\(=-1575\)