a: Kẻ PK vuông góc MN
\(S_{MNP}=\dfrac{1}{2}\cdot PK\cdot MN\)
\(S_{MIP}=\dfrac{1}{2}\cdot PK\cdot MI\)
=>\(\dfrac{S_{MNP}}{S_{MIP}}=\dfrac{MN}{MI}=\dfrac{5}{4}\)
=>\(S_{MIP}=60:\dfrac{5}{4}=48\left(cm^2\right)\)
b: Kẻ IH vuông góc MP
\(S_{MIJ}=\dfrac{1}{2}\cdot IH\cdot MJ\)
\(S_{MIP}=\dfrac{1}{2}\cdot IH\cdot MP\)
=>\(\dfrac{S_{MIJ}}{S_{MIP}}=\dfrac{MJ}{MP}=\dfrac{3}{4}\)
=>\(S_{MIJ}=36\left(cm^2\right)\)