Air, with stagnation conditions of 800 kPa and 100C, expands isentropically to a section of a duct

Question:

Air, with stagnation conditions of 800 kPa and 100°C, expands isentropically to a section of a duct where A1 = 20 cm2 and p1 = 47 kPa. Compute
(a) Ma1;
(b) The throat area; and
(c) M. At section 2, between the throat and section 1, the area is 9 cm2.
(d) Estimate the Mach number at section 2.