a cylindrical concrete sewer pipe is to be cast so that the concrete is uniformly 75mm thick while the cross section of the concrete is 0.164m2(thats sposed 2 be squared)
formulate and solve the simultaneous equations showing the relationship betwen the external radius, R, andthe internal radius r, of the pipe.

all workin out would be great thnx

2. Hello, jaswinder!

A cylindrical concrete sewer pipe is to be cast so that the concrete
is uniformly 75mm thick, while the cross section of the concrete is 0.164 m².
Formulate and solve the simultaneous equations showing the relationship
between the external radius, R, and the internal radius, r, of the pipe.

They're mixing millimeters and meters . . . beware!
. . 0.164 m² = 164,000 mm²

The difference of radii is 75: .R - r .= .75 . . r .= .R - 75 .[1]

The cross-sectional area is: .πR² - πr² .= .164,000 .[2]

Substitute [1] into [2]: .πR² - (R - 75)² .= .164,000

. . and we have: .150πR .= .5625π + 164,000

. . . . . . . . . . . . .5625p + 164,000
Therefore: . R .= .-------------------- . .385.5 mm
. . . . . . . . . . . . . . . . 150p

. . . . and: . r .= .310.5 mm